This question already has answers here:
Why use named function expressions?
(5 answers)
Closed 4 years ago.
Here is the code sample I have a question about:
var javascriptObject = {
functionName1: function functionName2() {
}
}
I understand the concept of an object in the javascript. I understand everything in the code sample except the functionName2 what is its purpose?
And I saw the code in the real life projects:
init: function init() {
init._base.call(this);
}
The code above does not work if I get rid from the second init. What does that second function name mean in javascript?
Object in JS are just name value pairs nothing more
var javascriptObject = {
functionName1: function functionName2() {
}
}
So what your doing is having a object which has a name of functionName1 which has the value of
function functionName2() {}
The name of the function stored in this value is functionName2 but this also could be omitted since it is not necessary to invoke the function.
For example you could run the function without the functionName2
var javascriptObject = {
functionName1: function () {
return 5;
}
};
var bar = javascriptObject.functionName1();
console.log(bar);
Related
This question already has answers here:
How to access the correct `this` inside a callback
(13 answers)
Closed 3 years ago.
Long-time .Net developer here, tasked with converting a bunch of old JS code to new ES6 JS modules. I'm trying to run the (you would think) simple code below, but when jumpToVideoNew is called, this.allowVidJump in the delegate function doesn't have access to the class property allowVidJump. I'm trying to set a simple timed delay so calling code can't hammer the jumpToVideoNew function repeatedly. I understand the concept that the variable loses scope, but I've tried setting _this = this; and using _this in the delegate as well with no success. Also tried passing a reference to the variable in to the function and accessing it that way, but also no luck. Spending 2 hours on something this simple is reminding me why I steer clear of javascript when possible.
export class WebUtility {
constructor() {
this.allowVideoJump = true;
this.delay = function () { this.allowVidJump = true; };
}
jumpToVideoNew() {
if (this.allowVideoJump) {
this.allowVideoJump = false;
setTimeout(this.delay, 1000);
}
}
}
Use an anonymous arrow function
The function keyword in JS creates a new scope as well as a new this (the function you just defined === this), so this.allowVidJump is essentially (function() {}).allowVidJump in that scope
Try something like this:
export class WebUtility {
constructor() {
this.allowVideoJump = true;
this.delay = () => { this.allowVidJump = true; }; // anonymous lambda
}
jumpToVideoNew() {
if (this.allowVideoJump) {
this.allowVideoJump = false;
setTimeout(this.delay, 1000);
}
}
}
This question already has answers here:
Referencing "this" inside setInterval/setTimeout within object prototype methods [duplicate]
(2 answers)
How to return value from an asynchronous callback function? [duplicate]
(3 answers)
Closed 5 years ago.
This question is from an written test for a company. It looks very confusing. I thought it will print whatever this.name is set to. Bu when I typed the code it shows nothing. I have little knowledge about closures and I think it is related to the problem. I want a little explanation here.
function dd(name) {
this.name = name;
this.go = function() {
setInterval(function() {
return this.name;
}, 2000)
}
}
var tt = new dd("corolla");
tt.go()
You can't get the return value from setInterval in this way. Try with a callback as in the following snippet
function dd(name)
{
this.name=name;
console.log( name );
var _this = this;
this.go=function(cb)
{
setInterval(function() {
cb(_this.name);
},1000)
}
}
var tt=new dd("corolla");
tt.go(function(ret) {
console.log( ret );
})
Also, please note that inside setInteval the value of this is not the same as in the otter function. That's why var _this=this;
This question already has answers here:
JavaScript closure inside loops – simple practical example
(44 answers)
Is there a way to wrap all JavaScript methods with a function?
(3 answers)
Closed 8 years ago.
Here's what I want to achieve:
var obj = {
something: 1,
someFunction: function () {
return 'hello';
}
};
wrap(obj).someFunction('hello'); // this should be different from obj.someFunction defined above
wrap(obj).something = 2; // this should still work
Basically, I want to 'wrap' an object and replace all the functions in it with something else.
Here's how I've defined the wrap function:
function hello (v) {
return 'Hello ' + v;
}
function wrap (oldObj) {
var newObj = {};
for (var k in oldObj)
Object.defineProperty(newObj, k, {
get: function () {
if (typeof oldObj[k] === 'function')
return hello;
return oldObj[k];
},
set: function (val) {
oldObj[k] = val;
}
});
return newObj;
}
(hello is just an example replacement function)
When I try to use this, everything in obj gets replaced with a function (i.e even obj.something, which was set to 1, is replaced with a function). I can't seem to find any issues with this code. I've tried debugging it and haven't found the issue yet.
What might be the issue? How else can I solve this problem?
Edit 1: I don't want to replace functions in the object itself, I want to create an entirely new object.
This question already has answers here:
var functionName = function() {} vs function functionName() {}
(41 answers)
Closed 9 years ago.
I see named functions exampled this way:
var clearClick = function() {
// do something
}
...and then used for binding like so:
$("#clear").bind(click, clearClick);
...or with the "shorthand" methodology thus:
$("#clear").click(clearClick);
But why not use a more "normal" (similar to other programming languages) construct like this:
function clearClick() {
// do something
}
It works the same, doesn't it? Is there any disadvantage to defining functions in this traditional way? Is the previous way just jQuerians flaunting their newfangledness?
This works Function expression
var clearClick = function() {
// do something
}
$("#clear").bind(click, clearClick);
This does not work Function expression. The order matters here.
$("#clear").bind(click, clearClick);
var clearClick = function() {
// do something
}
But when you declare your function using a function declaration the order does not matter.
One more advantage of the below syntax is that the function name appears in debugger.
function clearClick() {
// do something
}
One reason you might want to do it is how this works:
var clearClick;
$("#clear").click(clearClick);
clearClick = function() {
// do something
}
... lots of stuff in here ...
clearClick = function() {
// do something different
}
This question already has answers here:
How to execute a JavaScript function when I have its name as a string
(36 answers)
Closed 9 years ago.
I am passing function A's or B's name in a parameter based on the situation to another function C. How can I call it in function C?
if A is defined globally, then window["A"](). However, there's no need to do that in javascript. Just pass the function itself rather than its name:
function foo() {...}
// BAD
function callFunc(someName) { window[someName]() }
callFunc("foo")
// GOOD
function callFunc(someFunc) { someFunc() }
callFunc(foo)
Like this:
window[varName]()
assuming it is in global scope
If you have
function A() {}
function B() {}
then you can do
function C(parm) {
parm();
}
if you call it with C(A) or C(B)
DEMO
You could assign the functions to properties of an object. Then in your executing function reference the property by name given the parameter passed to the function.
var myFuncs = {
a: function(){
alert("Hello");
},
b: function(){
alert("Goodbye");
}
};
function execute(name){
myFuncs[name]();
}
execute("a");
execute("b");
Working Example http://jsfiddle.net/ud6BS/