Why “this” refers to Window in forEach in javascript? [duplicate]

Answer 1

The function you've passed into forEach does not have the same context as your object. The forEach (as well as map etc) functions run detached from any object, so functions passed into them are executed in global scope by default.

You could be explicit and fix that in one of two ways.

1. give the forEach a context to run in (as suggested by every other answer)

This uses code like:

var arr = [...];
var iterator = function(e) { console.log(this); };
arr.forEach(iterator, this);

2. make your iteration function explicitly bound to your object first

this uses code like:

var arr = [...];
var iterator = function(e) { console.log(this); };
var iteratorWithThisContext = iterator.bind(this);
arr.forEach(iteratorWithThisContext);

The bind() function is a core javascript function for taking any function, and any context, and returning a new function that will always execute with the specified context when called, no matter who's doing the calling, or when:

var fn = function() { console.log(this); }
fn(); // window

var fndoc = fn.bind(document);
fndoc(); // document

var arr = [];
var fnarr = fn.bind(arr);
fnarr(); // the array