CODEWITHSUNDEEP
javascriptscope
Sonevol
Sonevol

Reputation: 290

Unable to understand certain concepts in JavaScript

In the website the following lines are given:

Your global variables (or functions) can overwrite window variables (or functions). Any function, including the window object, can overwrite your global variables and functions.

I am unable to understand what this says.

Upvotes: 2

Views: 53

Answers (2)

Jack Guy
Jack Guy

Reputation: 8523

The browser puts certain "global" (i.e. accessible anywhere in any file) functions and variables on the window object. One such example is the function window.setTimeout, which executes its argument after a given delay.

You can also access these global window.* variables without the window prefix at all, i.e.

window.setTimeout === setTimeout

That means if you assign to a global variable with a conflicting name, you can 'override' the browser defaults -

window.setTimeout === setTimeout
setTimeout = 'myString'
window.setTimeout === 'myString'

That's why it's generally best practice not to create variables in the global (window) scope.

Upvotes: 2

Dekel
Dekel

Reputation: 62566

Above that paragraph you can find this:

Global Variables in HTML With JavaScript, the global scope is the complete JavaScript environment.

In HTML, the global scope is the window object. All global variables belong to the window object.

Combined with the quote in your question - it means that because the global scope is actually the window object - it's possible to override global functions/variables.

Here is an example:

console.log(window.Math.PI);

Math = {
  PI: 5
}

console.log(Math.PI);

Upvotes: 2

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