I use eval() to execute javascript that is returned by an ajax request from the server. However, I cant call a function that was created with eval() and got a ReferenceError: function is not defined.
Is it something normal that functions inside a javascript that was executed with eval() cannot be accessed? Is there a way to access such functions?
I think this simple jsFiddle illustrate the problem: http://jsfiddle.net/M2GLs/
The created function isn't in the correct scope. So your onclick can't 'see' it. Use
window.addFeatureToTable = function() {
// definition
}
to force it in the window-scope.
Working JsFiddle
To answer your question in the comment:
What you actualy have is something like this code:
function a()
{
function b(where) {
alert('b can be called inside a, but not outside, we are now ' + where);
}
b('inside');
}
a();
b('outside');
b is defined in the scope of a, and can only be accessed within this scope (demo). In your case the function-definition is within an eval, but the same rule aplies there. In that case within the scope of function(r). You can't access the scope of this function from within the a.onclick, so you have to change the function-definition. Alternatively you can bind the on-click just after the eval (jsFiddle), since it is then still in scope:
js = "function someFunction() { alert('function called') }"
eval(js)
document.getElementById('myA').onclick = someFunction;
Related
I'm trying to create a function that returns a callback, which when called, will access the callers local scope parameters.
Consider the following code:
function caller() {
let param = "original scope param.";
let wrapped = callee();
eval(wrapped.toString())(); // Works
wrapped(); // Doesn't work
}
function callee() {
return () => eval("console.log('Im accessing ' + param)");
}
caller()
calling eval in the caller function works, but I don't control that function, so I can't make it eval my output.
If I could access the Scope Chain, my problem would be solved, but I didn't find anything that does that. Any help would be appreciated, even if the solution is very dirty.
I'm using PhantomJS v2.0 and CasperJS 1.1.0-beta3. I want to query a specific part inside the page DOM.
Here the code that did not work:
function myfunc()
{
return document.querySelector('span[style="color:#50aa50;"]').innerText;
}
var del=this.evaluate(myfunc());
this.echo("value: " + del);
And here the code that did work:
var del=this.evaluate(function()
{
return document.querySelector('span[style="color:#50aa50;"]').innerText;
});
this.echo("value: " + del);
It seems to be the same, but it works different, I don't understand.
And here a code that did also work:
function myfunc()
{
return document.querySelector('span[style="color:#50aa50;"]').innerText;
}
var del=this.evaluate(myfunc);
this.echo("value: " + del);
The difference here, I call the myfunc without the '()'.
Can anyone explain the reason?
The problem is this:
var text = this.evaluate(myfunc());
Functions in JavaScript are first class citizen. You can pass them into other functions. But that's not what you are doing here. You call the function and pass the result into evaluate, but the result is not a function.
Also casper.evaluate() is the page context, and only the page context has access to the document. When you call the function (with ()) essentially before executing casper.evaluate(), you erroneously try to access the document, when it is not possible.
The difference to casper.evaluate(function(){...}); is that the anonymous function is defined and passed into the evaluate() function.
There are cases where a function should be called instead of passed. For example when currying is done, but this is not applicable to casper.evaluate(), because it is sandboxed and the function that is finally run in casper.evaluate() cannot use variables from outside. It must be self contained. So the following code will also not work:
function myFunc2(a){
return function(){
// a is from outer scope so it will be inaccessible in `evaluate`
return a;
};
}
casper.echo(casper.evaluate(myFunc2("asd"))); // null
You should use
var text = this.evaluate(myfunc);
to pass a previously defined function to run in the page context.
It's also not a good idea to use reserved keywords like del as variable names.
I have several script blocks depend on each other. I need to perform them in one scope.
My attempt:
var scopeWrapper = {};
with(scopeWrapper) {
(function() {
this.run = function(code) {
eval(code);
};
}).call(scopeWrapper);
}
scopeWrapper.run('function test() { alert("passed"); }');
scopeWrapper.run('test();');
I get 'test is not defined' error. It seems that the code is executed in different scopes.
Why is this happening?
Edit: Bergi pointed out my original answer was wrong, he is correct. Since eval runs in its own scope and the function constructor still runs in function scope according to the spec this is not possible with either.
While I have done this sort of thing myself several times with node.js using the vm module where you get much finer grain of control over where your code executes, it seems browsers require a different approach.
The only way you can share variables in such a way is to do so in the global scope of JavaScript execution (possibly, in an iframe). One way you could do this is script tag injection.
function run(code){
var sc = document.createElement("script");
sc.setAttribute("type","text/javascript");
sc.innerHTML = code;
document.body.appendChild(sc);
}
run("var x = 5");
run("document.write(x)");
(here is this code in action)
As for the scope wrapper, instead of injecting them in the same frame inject them in another iframe. That will scope their window object to that iframe and will allow you to share context.
I humbly apologize for my previous answer, I misread the spec. I hope this answer helps you.
I'm leaving my previous answer here because I still believe it provides some insight into how eval and the Function constructor work.
When running code in non-strict mode eval runs in the current context of your page
After your function declaration is done, the scope it was declared in dies, and with it the function.
Consider using the Function constructor and then .calling it
In your case that would be something like:
var scopeWrapper = {};
scopeWrapper.run = function(code){
var functionToRun = new Function(code);
functionToRun.call(scopeWrapper);
}
scopeWrapper.run('this.test = function() { alert("passed"); }');
scopeWrapper.run("this.test()")
Here is a reference directly from the spec:
If there is no calling context or if the eval code is not being evaluated by a direct call (15.1.2.1.1) to the eval function then,
Initialize the execution context as if it was a global execution context using the eval code as C as described in 10.4.1.1.
If this code is run in the node.js consider using the vm module. Also note that this approach is still not secure in the way it'll allow code you run to change your code.
test only exists in the scope of this.run and only at call time :
// global scope
(function(){
// local scope (equivalent of your "run" function scope)
eval('function f(){};');
console.log(f); // prints "function f(){}"
})();
console.log(f); // prints "ReferenceError: f is not defined"
Each call of run creates a new scope in which each code is evaluated separately.
I have a script that I didn't write already running on a page. I'd like to, in a script I did write, be able to execute a function from the original script. Here's a simplified example of what I'm trying to do:
(function ($) {
$.fn.myExistingFunction = function (options) {
function doMyThing(text) {
alert(text);
}
}
}(jQuery));
jQuery(document).ready(function($) {
$.fn.myExistingFunction.doMyThing("alert text");
});
However, when I run this, I get the console output:
Uncaught TypeError: Object function (options) {
function doMyThing(text) {
alert(text);
}
} has no method 'doMyThing'
But it clearly has the method! I can see it right there. What am I getting wrong here?
You can only access that method from the scope of the plugin function. It is not defined in the global scope.
So you can't call that function. All you can do in your code is call functions that are available through what's called the scope chain where the function is called. In your case that is everything that is either defined in your function($){} or in global scope. But the function in the plugin is neither.
When you call $.fn.myExistingFunction.doMyThing you are treating doMyThing like an field in the myExistingFunction object. But actually it is defined inside the function. Maybe this code makes it clearer:
$.fn.myExistingFunction = function (options) {
var doMyThing = function(text) {
alert(text);
}
var hi = "hello";
}
In hi and doMyThing are local variables in the scope of myExistingFunction. If the plugin wasn't designed to expose the functionality to external code you can't access the variables.
An example of a plugin that was designed to expose some of its internal functions would be the jQuery UI datepicker (documentation). It needs functions like parseDate and formatDate interally, but these utility functions are likely to be useful for general development as well, which is why they have been added to the datepicker object explicitly.
I think your code needs a major rewriting, 'cause as it is it will never work, in fact your function doMyThing is not a property of $.fn.myExistingFunction, it is simply declared inside of it, and due to how the scope works in javascript, you'll never be able to call it.
*Is there a way to call a function defined inside another function in javaSCRIPT? For example:
window.onload() = function() {
function my_function(){
print("Blah");
};
};
function function_two(){
my_function();
};
Is there a way to do something like the above (calling my_function in function_two even though it's defined inside the window.onload() function)? In my actual code, which also uses the raphael.js library, I'm trying to write a button in HTML, which using the onClick function, calls a function(like function_two) that runs the function defined in window.onload() (like my_function). However the console says that the my_function is undefined.
The scope of the function is the core issue here, as Zeychin and Trevor have said. I thought I'd offer another way of handling it. Basically, you can set your function to a variable that's in a higher scope (that is, accessible to both the onload and function_two functions), while defining it inside the onload function as you originally have:
var myFunction; //This is the placeholder which sets the scope
window.onload() = function() {
myFunction = function() { //Assign the function to the myFunction variable
print('blah');
}
}
function function_two() {
myFunction();
}
This might be handy if you only know the information you need for myFunction once you're in the onload event.
You can not do what you are asking to do.
The function my_function()'s scope is only within the anonymous function, function(). It falls out of scope when the method is not executing, so this is not possible.
Trevor's answer is the way to do this.
window.onload = function() {
my_function()
};
function my_function(){
alert("Blah");
};
function function_two(){
my_function();
};