这个“ []”在做什么？

Question

Below is an extract from my textbook.

I have a question about the use of [] here in window.history[type]() . I can tell that it's separating the object name(window) and the variable(type) so that they can be recognized as separate things but is there a name for this use of []? I performed a google search but nothing came up.

$(function() {
//omitted
['back', 'forward'].forEach(function(type) {
  $('.' + type).click(function() {
    window.history[type]();
    });
  });
});

Answer 1

This is property/method access using bracket notation . In Javascript, you can access the properties of an object using the dot notation:

myObj.prop

Or the bracket notation:

myObj['prop']

When you dynamically construct the properties, however, you have no choice but to use bracket notation:

window.history['forward']()

is the same as

window.history.forward()

Here you are iterating on the forward and back properties, and the bracket notation is used to call the functions from their string names on window.history .

Here is the doc linked by @Teemu