Global variables in Javascript and ESLint - javascript

I have got multiple javascript files and I have defined some global variable in a file which loads before the others.
As a consequence all of the files loaded after the first have access to the global variable.
However ESLint shows the global variable as "not defined". I don't want to change the rules of ESLint and I would like to find an elegant way to get rid of these error messages.
Any clue?
Thanks

I don't think hacking ESLint rules per file is a great idea.
You should rather define globals in .eslintrc or package.json.
For .eslintrc:
"globals": {
"angular": true
}
For package.json:
"eslintConfig": {
"globals": {
"angular": true
}
}
Check https://eslint.org/docs/user-guide/configuring/language-options#specifying-globals

You can add globals either per file or in your config.
If you don't want to change your config, you'll have to add the used globals in every file.
To specify globals using a comment inside of your JavaScript file, use the following format:
/* global var1, var2 */
This defines two global variables, var1 and var2. If you want to optionally specify that these global variables should never be written to (only read), then you can set each with a false flag:
/* global var1:false, var2:false */
http://eslint.org/docs/2.0.0/user-guide/configuring#specifying-globals

Related

new URLPattern raises error in react "'URLPattern' is not defined" [duplicate]

I have got multiple javascript files and I have defined some global variable in a file which loads before the others.
As a consequence all of the files loaded after the first have access to the global variable.
However ESLint shows the global variable as "not defined". I don't want to change the rules of ESLint and I would like to find an elegant way to get rid of these error messages.
Any clue?
Thanks
I don't think hacking ESLint rules per file is a great idea.
You should rather define globals in .eslintrc or package.json.
For .eslintrc:
"globals": {
"angular": true
}
For package.json:
"eslintConfig": {
"globals": {
"angular": true
}
}
Check https://eslint.org/docs/user-guide/configuring/language-options#specifying-globals
You can add globals either per file or in your config.
If you don't want to change your config, you'll have to add the used globals in every file.
To specify globals using a comment inside of your JavaScript file, use the following format:
/* global var1, var2 */
This defines two global variables, var1 and var2. If you want to optionally specify that these global variables should never be written to (only read), then you can set each with a false flag:
/* global var1:false, var2:false */
http://eslint.org/docs/2.0.0/user-guide/configuring#specifying-globals

Webpack have trouble with scopes

There are several modules that are connected to app.js, for example the code that is inside:
var test = "TEST";
Here is my webpack.config:
module.exports = {
entry: './src/app.js',
output: {
filename: './dist/bundle.js'
}
};
The problem is that when I try to call my test variable in the developer console, I get an error:
Something about the scope, when I connect app.js directly - everything works, what's the problem and how to fix it?
Yes, this is a scope problem. There are two ways to fix this:
Instead of using var, use window.. (window.test = "TEST";)
Forget var (dosen't work in strict mode).test = "TEST";
Before the <script src="bundle.js"></script>, declare test (var test;) and then forget var.
Hope this is the anwser you're looking for.
The default functionality of webpack is to scope files that are passed in to its configuration, see documentation here: https://webpack.js.org/configuration/output/
This means that if you set a var in the file, then bundle it with webpack, it will become available only within its scope which, in this case, is the app.js file. If you open the file in your browser by itself, no scoping will take place hence why you don't have any issues when viewing directly.
If you need to access that test variable outside of the file, you'll have to turn it into a global variable, otherwise it will remain scoped within the bundle.js file created from webpack.

How to change an IIFE with an argument to ES6. [duplicate]

I am using Grunt as my Build Tool and ESLint as my linting tool for an app I am working on. I am also using the Underscore Node package, and have made use of it in my app. Unfortunately, when I run ESLint on my code, it thinks that _ is an undefined variable in the following line:
return _.pluck(objects, nameColumn);
This is the error it is giving me:
78:21 error "_" is not defined no-undef
I would prefer not to disable the no-undef rule for ESLint, and I have tried installing the Underscore plugin, but I am still receiving this error. If anyone else has any ideas for what to try with this, I would be very appreciative!
If there is any further information I can give that would help anyone with helping me get this figured out, just let me know!
The official documentation should give you an idea on how to fix this.
Any reference to an undeclared variable causes a warning, unless the variable is explicitly mentioned in a /*global ...*/ comment, or specified in the globals key in the configuration file.
The easiest fix would be to add
/* global _ */
at the top of your file.
Or better, explicitly specify that the variable is read-only, to disallow overwriting the variable:
/* global _:readonly */
But since you'll have to do that for each new js file, it can get annoying. If you are using underscore often, I'd suggest to add globals to your .eslintrc file, for example:
{
"globals": {
"_": "readonly"
}
}
And save this as .eslintrc in your project root, or optionally in your user home directory. Although some say the latter not recommended, it can sometimes be convenient, but you have to remember that you have it there :)
Explanation of the above rule: "_": "readonly" (used to be "_": false, now deprecated) means that a variable named _ tells eslint that this variable is defined globally and it will not emit any no-undef errors for this variable. As #sebastian pointed out, "readonly" (or false - deprecated) means that the variable can't be overwritten, so the code _ = 'something else' would yield an error no-global-assign. If you were to instead use "_": "writable" (or "_": true - deprecated), this means that the value can be re-assigned and the previously mentioned error will not occur.
But keep in mind that this will only happen if you assign directly to the global variable as I have shown in the example. You can still shadow it and eslint won't say anything. For example, these snippets wouldn't yield the no-global-assign:
const _ = 'haha I broke your _'
or as function argument name, e.g.
function (_) {
console.log(_, 'might not be the _ you were looking for')
}
If you are using jest for testing - in your environment - in eslintrc.json
"env":{
"jest":true
}

Ignoring a global variable in JSHint

I have a global variable called Filters that is loaded before anything else, but JSHint tells me it's undefined in all files that use Filters. Of course, JSHint does not know the loading order (and yes, the order is enforced), so how would it know?
I tried adding it to the globals:
"globals": {
"Filters": false
}
And that had no effect, so I tried:
"predef": [ "Filters" ]
Again, no effect.
These are also present:
"undef" : true,
"latedef" : false,
What am I missing here?
In this example, I would normally just put the following at the top of my files:
/* globals Filters */
I prefer to specify globals on a per file basis.

Configure a generic jQuery plugin with Browserify-shim?

I'm using browserify-shim and I want to use a generic jQuery plugin. I have looked over the Browserify-shim docs multiple times and I just can't seem to understand what's going on and/or how it knows where to put plugins, attach to the jQuery object etc. Here's what my package.json file looks like:
"browser": {
"jquery": "./src/js/vendor/jquery.js",
"caret": "./src/js/vendor/jquery.caret.js"
},
"browserify-shim": {
"caret": {
"depends": ["jquery:$"]
}
}
According the the example given on the browserify-shim documentation, I don't want to specify an exports because this plugin (and most if not all jQuery plugins) attach themselves to the jQuery object. Unless I'm doing something wrong above, I don't understand why it doesn't work (I get an error telling me the function is undefined) when I use it. See below:
$('#contenteditable').caret(5); // Uncaught TypeError: undefined is not a function
So my question is, how does one configure a generic jQuery plugin (which attaches itself to the jQuery object) with browserify and browserify-shim?
After revisiting this and trying some more things, I finally wrapped my head around what browserify-shim is doing and how to use it. For me, there was one key principle I had to grasp before I finally understood how to use browserify-shim. There are basically two ways to use browserify-shim for two different use cases: exposing & shimming.
Background
Let's say you want to just drop in a script tag in your markup (for testing or performance reasons like caching, CDN & the like). By including a script tag in the markup the browser will hit the script, run it, and most likely attach a property on the window object (also known as a global in JS). Of course this can be accessed by either doing myGlobal or window.myGlobal. But there's an issue with either syntax. It doesn't follow the CommonJS spec which means that if a module begins supporting CommonJS syntax (require()), you're not able to take advantage of it.
The Solution
Browserify-shim allows you to specify a global you'd like "exposed" through CommonJS require() syntax. Remember, you could do var whatever = global; or var whatever = window.global; but you could NOT do var whatever = require('global') and expect it to give you the right lib/module. Don't be confused about the name of the variable. It could be anything arbitrary. You're essentially making a global variable a local variable. It sounds stupid, but its the sad state of JS in the browser. Again, the hope is that once a lib supports CommonJS syntax it will never attach itself via a global on the window object. Which means you MUST use require() syntax and assign it to a local variable and then use it wherever you need it.
Note: I found variable naming slightly confusing in the browserify-shim docs/examples. Remember, the key is that you want to include a lib as if it were a properly behaving CommonJS module. So what you end up doing is telling browserify that when you require myGlobal require('myGlobal') you actually just want to be given the global property on the window object which is window.myGlobal.
In fact, if you're curious as to what the require function actually does, it's pretty simple. Here's what happens under the hood:
var whatever = require('mygGlobal');
becomes...
var whatever = window.mygGlobal;
Exposing
So with that background, let's see how we expose a module/lib in our browserify-shim config. Basically, you tell browserify-shim two things. The name you want it accessible with when you call require() and the global it should expect to find on the window object. So here's where that global:* syntax comes in. Let's look at an example. I want to drop in jquery as a script tag in index.html so I get better performance. Here's what I'd need to do in my config (this would be in package.json or an external config JS file):
"browserify-shim": {
"jquery": "global:$"
}
So here's what that means. I've included jQuery somewhere else (remember, browserify-shim has no idea where we put our tag, but it doesn't need to know), but all I want is to be given the $ property on the window object when I require the module with the string parameter "jquery". To further illustrate. I could also have done this:
"browserify-shim": {
"thingy": "global:$"
}
In this case, I'd have to pass "thingy" as the parameter to the require function in order to get an instance of the jQuery object back (which it's just getting jQuery from window.$):
var $ = require('thingy');
And yes, again, the variable name could be anything. There's nothing special about $ being the same as the global property $ the actual jQuery library uses. Though it makes sense to use the same name to avoid confusion. This ends up referencing the the $ property on the window object, as selected by the global:$ value in the browserify-shim object in package.json.
Shimming
Ok, so that pretty much covers exposing. The other main feature of browserify-shim is shimming. So what's that? Shimming does essentially the same thing as exposing except rather than including the lib or module in HTML markup with something like a script tag, you tell browserify-shim where to grab the JS file locally. There's no need to use the global:* syntax. So let's refer back to our jQuery example, but this time suppose we are not loading jQuery from a CDN, but simply bundling it with all the JS files. So here's what the config would look like:
"browser": {
"jquery": "./src/js/vendor/jquery.js", // Path to the local JS file relative to package.json or an external shim JS file
},
"browserify-shim": {
"jquery": "$"
},
This config tells browserify-shim to load jQuery from the specified local path and then grab the $ property from the window object and return that when you require jQuery with a string parameter to the require function of "jquery". Again, for illustrative purposes, you can also rename this to anything else.
"browser": {
"thingy": "./src/js/vendor/jquery.js", // Path to the local JS file relative to package.json or an external shim JS file
},
"browserify-shim": {
"thingy": "$"
},
Which could be required with:
var whatever = require('thingy');
I'd recommend checking out the browserify-shim docs for more info on the long-hand syntax using the exports property and also the depends property which allows you to tell browserify-shim if a lib depends on another lib/module. What I've explained here applies to both.
Anonymous Shimming
Anonymous shimming is an alternative to browserify-shim which lets you transform libs like jQuery into UMD modules using browserify's --standalone option.
$ browserify ./src/js/vendor/jquery.js -s thingy > ../dist/jquery-UMD.js
If you dropped that into a script tag, this module would add jQuery onto the window object as thingy. Of course it could also be $ or whatever you like.
If however, it's requireed into your browserify'd app bundle, var $ = require("./dist/jquery-UMD.js");, you will have jQuery available inside the app without adding it to the window object.
This method doesn't require browserify-shim and exploits jQuery's CommonJS awareness where it looks for a module object and passes a noGlobal flag into its factory which tells it not to attach itself to the window object.
For everyone, who is looking for a concrete example:
The following is an example of package.json and app.js files for a jQuery plugin that attaches itself to the jQuery/$ object, e.g.: $('div').expose(). I don't want jQuery to be a global variable (window.jQuery) when I require it, that's why jQuery is set to 'exports': null. However, because the plugin is expecting a global jQuery object to which it can attach itself, you have to specify it in the dependency after the filename: ./jquery-2.1.3.js:jQuery. Furthermore you need to actually export the jQuery global when using the plugin, even if you don't want to, because the plugin won't work otherwise (at least this particular one).
package.json
{
"name": "test",
"version": "0.1.0",
"description": "test",
"browserify-shim": {
"./jquery-2.1.3.js": { "exports": null },
"./jquery.expose.js": { "exports": "jQuery", "depends": [ "./jquery-2.1.3.js:jQuery" ] }
},
"browserify": {
"transform": [
"browserify-shim"
]
}
}
app.js
// copy and delete any previously defined jQuery objects
if (window.jQuery) {
window.original_jQuery = window.jQuery;
delete window.jQuery;
if (typeof window.$.fn.jquery === 'string') {
window.original_$ = window.$;
delete window.$;
}
}
// exposes the jQuery global
require('./jquery.expose.js');
// copy it to another variable of my choosing and delete the global one
var my_jQuery = jQuery;
delete window.jQuery;
// re-setting the original jQuery object (if any)
if (window.original_jQuery) { window.jQuery = window.original_jQuery; delete window.original_jQuery; }
if (window.original_$) { window.$ = window.original_$; delete window.original_$; }
my_jQuery(document).ready(function() {
my_jQuery('button').click(function(){
my_jQuery(this).expose();
});
});
In the above example I didn't want my code to set any globals, but I temporarily had to do so, in order to make the plugin work. If you only need jQuery, you could just do this and don't need any workaround: var my_jQuery = require('./jquery-2.1.3.js'). If you are fine with your jQuery being exposed as a global, then you can modify the above package.json example like so:
"browserify-shim": {
"./jquery-2.1.3.js": { "exports": "$" },
"./jquery.expose.js": { "exports": null, "depends": [ "./jquery-2.1.3.js" ] }
Hope that helps some people, who were looking for concrete examples (like I was, when I found this question).
Just for completeness, here is a method that exploits jQuery's CommonJS awareness to avoid having to worry about polluting the window object without actually needing to shim.
Features
jQuery included in the bundle
plugin included in the bundle
no pollution of the window object
Config
In ./package.json, add a browser node to create aliases for the resource locations. This is purely for convenience, there is no need to actually shim anything because there is no communications between the module and the global space (script tags).
{
"main": "app.cb.js",
"scripts": {
"build": "browserify ./app.cb.js > ./app.cb.bundle.js"
},
"browser": {
"jquery": "./node_modules/jquery/dist/jquery.js",
"expose": "./js/jquery.expose.js",
"app": "./app.cb.js"
},
"author": "cool.blue",
"license": "MIT",
"dependencies": {
"jquery": "^3.1.0"
},
"devDependencies": {
"browserify": "^13.0.1",
"browserify-shim": "^3.8.12"
}
}
Method
Because jQuery is CommonJS-aware these days, it will sense the presence of the module object provided by browserify and return an instance, without adding it to the window object.
In the app, require jquery and add it to the module.exports object (along with any other context that needs to be shared).
Add a single line at the start of the plugin to require the app to access the jQuery instance it created.
In the app, copy the jQuery instance to $ and use jQuery with the plugin.
Browserify the app, with default options, and drop the resulting bundle into a script tag in your HTML.
Code
app.cb.js
var $ = module.exports.jQuery = require("jquery");
require('expose');
$(document).ready(function() {
$('body').append(
$('<button name="button" >Click me</button>')
.css({"position": "relative",
"top": "100px", "left": "100px"})
.click(function() {
$(this).expose();
})
);
});
at the top of the plugin
var jQuery = require("app").jQuery;
in the HTML
<script type="text/javascript" src="app.cb.bundle.js"></script>
Background
The pattern used by jQuery is to call it's factory with a noGlobal flag if it senses a CommonJS environment. It will not add an instance to the window object and will return an instance as always.
The CommonJS context is created by browserify by default. Below is an simplified extract from the bundle showing the jQuery module structure. I removed the code dealing with isomorphic handling of the window object for the sake of clarity.
3: [function(require, module, exports) {
( function( global, factory ) {
"use strict";
if ( typeof module === "object" && typeof module.exports === "object" ) {
module.exports = factory( global, true );
} else {
factory( global );
}
// Pass this if window is not defined yet
} )( window, function( window, noGlobal ) {
// ...
if ( !noGlobal ) {
window.jQuery = window.$ = jQuery;
}
return jQuery;
}) );
}, {}]
The best method I found is to get things working in the node module system and then it will work every time after browserify-ing.
Just use jsdom to shim the window object so that the code is isomorphic. Then, just focus on getting it to work in node. Then, shim any traffic between the module and global space and finally browserify it and it will just work in the browser.
I was using wordpress. Hence, I was kind of forced to use the wordpress core's jQuery, available in window object.
It was generating slick() not defined error, when I tried to use slick() plugin from npm. Adding browserify-shim didn't help much.
I did some digging and found out that require('jquery') was not consistent always.
In my theme javascript file, it was calling the wordpress core's jquery.
But, in slick jquery plugin it was calling the latest jquery from node modules.
Finally, I was able to solve it. So, sharing the package.json and gulpfile configuration.
package.json:
"browserify": {
"transform": [
"browserify-shim"
]
},
"browserify-shim": {
"jquery": "global:jQuery"
},
gulpfile.babel.js:
browserify({entries: 'main.js', extensions: ['js'], debug: true})
.transform(babelify.configure({
presets: ["es2015"]
}))
.transform('browserify-shim', {global: true})
Doing transform 'browserify-shim' was crucial part, I was missing earlier. Without it browserify-shim was not consistent.

Categories