This question already has answers here:
alias to chrome console.log
(3 answers)
Closed 9 years ago.
Why I can't make this in javascript:
var log = console.log;
log(123);
And how to achieve that?
In JavaScript, the value of this depends on how a function is called.
Inside log(), this is undefined in strict mode or the default object otherwise (that's window in a browser).
Inside console.log(), this is console.
The log function, presumably, depends on having access to the console object.
You can write a wrapper function instead:
function log() {
console.log.apply(console, arguments);
}
In sufficiently modern browsers, you can generate that function using bind.
var log = console.log.bind(console);
Related
This question already has answers here:
How to disable JavaScript function calls from the browser console?
(6 answers)
Closed 3 years ago.
Alright so I've a function (not exactly the one written bellow, that one is just an example)
function test()
{
alert("Hello");
}
Now the problem is that people are able to go into console and just type "test()" and call the function.
Is there a way to prevent this? I dont want of people to call functions from the console.
You can narrow the context that your function is executed in, eg:
(function() {
function test() { /* Do anything */ }
test();
// Call test anywhere here
})()
test(); // Error: test is undefined
This question already has answers here:
How does the "this" keyword in Javascript act within an object literal? [duplicate]
(4 answers)
Closed 4 years ago.
Was doing some dirty things to Array.prototype when I ran into this:
Array.prototype.hook_pop = function(callback) {
var base_pop = this.pop.bind(this); //<-- this works
var base_pop = this.pop; //<-- this doesn't work
this.pop = function() {
var ret = base_pop();
callback(ret, this);
return ret;
}
}
Initially I tried using the non-working option and got an error "Uncaught TypeError: Cannot convert undefined or null to object".
The way I've understood it, unless otherwise bound, "this" should point to the object through which the method is called from, in this case the array instance. When called on the same object though, either way, "this" should be the same when being passed to the pop function, whether its bound or not. Why doesn't the second option work?
var ret = base_pop();
In this line you're invoking base_pop() by itself, and not as a method of any object. Because of this, its this value isn't set.
This question already has answers here:
How does the "this" keyword in Javascript act within an object literal? [duplicate]
(4 answers)
Closed 5 years ago.
Im reading through the YDKJS books and I thought I understood lexical this for the most part.
However there is a section with code that shows this:
var obj = {
id: "awesome",
cool: function coolFn() {
console.log( this.id );
}
};
var id = "not awesome";
obj.cool(); // awesome
setTimeout( obj.cool, 100 ); // not awesome
Ok so the first obj.cool() makes sense of course....but why is the setTimeout printing not awesome.....I mean it's still calling obj.cool() which this refers to it's own objects id?
Or does setTimeout get called as another function that calls obj.cool()? but even in that case (Which I tried calling obj.cool() inside another function that also had an id property and it still printed the right one......so why would the this change with setTimeout?
Since the OBJ.COOL function is passed by reference, you are not actually passing the context object with it. The function gets new invocation context and executes on the WINDOW object, which now has a property called ID which was defined earlier.
This question already has answers here:
In Javascript, why is the "this" operator inconsistent?
(8 answers)
How does the "this" keyword work, and when should it be used?
(22 answers)
Closed 9 years ago.
hi i am a little confusion on how exactly this works in javascript.Based on this example:
var myFunction = function(){
function testMe(){
console.log(this) --------> DOMwindow
}
console.log(this) ---------> myFunction
}
var myvariable = new myFunction();
What is happening here?
The value this references depends on circumstances. Any unscoped (i.e. not in an object) function call will have this = window (DOMWindow, if you prefer). Anything that is part of a prototype, or has been changed using apply or bind, will have this as that object ("itself", if you prefer).
So, to illustrate. When you are instantiating using the new keyword, your function automatically inherits this as itself. When you call an IETF within it, this within this IETF will point to the global scope.
If you would like to avoid this, instead of calling testMe literally, you can always do this:
var myFunction = function() {
var testMe = function() {
console.log(this);
}
testMe.bind(this);
}
Which will, in turn, have this within testMe use the object as it should.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
If Javascript has first-class functions, why doesn’t this work?
In Chrome, the following produces Uncaught TypeError: Illegal invocation:
g = console.log;
g(1);
Why does this happen, and why can't I treat console.log like a regular object?
It happens because you've lost the reference to console. You're just calling log directly, with no context. You can call the function in the context of console to make it work:
g.call(console, 1);
Or, to save you from doing that every time, you can bind the function back to the console object:
var g = console.log.bind(console);
References:
Function.prototype.call
Function.prototype.apply (not used here, but still of interest)
Function.prototype.bind