javascript - When does console.log get executed? - Stack Overflow

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I'm trying to debug some pretty simple Javascript using console.log, but it's outputting values for variables that are not changed until after the console.log call, when the variables are 'class' members (Chrome 22, Firefox 16).

An example of what I expect to happen would be like this:

var a = 1;
console.log(a);
a += 20;

//console output says a is 1

But if the variable is a 'class' member:

var a = new myClass(1);
console.log(a);
a.x += 20;

//console output says a.x is 21

If the console does not log the value as it exists when the log is called, when does it finally decide to log the value, and how can I work around this!?

fwiw here is the entirety of the code:

function myClass() {
    myClass.myClass.apply(this, arguments);
    if (this.constructor === myClass) this.myClass.apply(this, arguments);
};
myClass.myClass = function () {};
myClass.prototype.myClass = function (x_) {
    if (x_ === undefined) x_ = 0;
    this.x = x_;
}

var a = new myClass(1);
console.log(a);
a.x += 20;

I'm trying to debug some pretty simple Javascript using console.log, but it's outputting values for variables that are not changed until after the console.log call, when the variables are 'class' members (Chrome 22, Firefox 16).

An example of what I expect to happen would be like this:

var a = 1;
console.log(a);
a += 20;

//console output says a is 1

But if the variable is a 'class' member:

var a = new myClass(1);
console.log(a);
a.x += 20;

//console output says a.x is 21

If the console does not log the value as it exists when the log is called, when does it finally decide to log the value, and how can I work around this!?

fwiw here is the entirety of the code:

function myClass() {
    myClass.myClass.apply(this, arguments);
    if (this.constructor === myClass) this.myClass.apply(this, arguments);
};
myClass.myClass = function () {};
myClass.prototype.myClass = function (x_) {
    if (x_ === undefined) x_ = 0;
    this.x = x_;
}

var a = new myClass(1);
console.log(a);
a.x += 20;

• javascript
• class
• logging
• console

Share Improve this question Follow asked Nov 4, 2012 at 11:52 iforce2diforce2d 8,27233 gold badges3333 silver badges4242 bronze badges

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1 Answer 1

Sorted by: Reset to default 9

Immediately, but the state of objects is fetched when you expand the object manually in console - not at the time of the logging.

By the time you expand it in your console, the code to add 20 has executed a long time ago (in relative terms) and it says x: 21

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