A brief discussion on js literals, access to object literals, and the usage of the keyword in

1: Literal meaning

Literal represents how to express the value. Generally, except for expressions, when assigning a value to a variable, the right side of the equal sign can be considered a literal.

Literals are divided into string literals, array literals and

object literals, in addition to function literals.

Example:

var test="hello world!";
"hello world!" is a string literal, and test is a variable name.

2: Object literals

Object literals have two access methods: the example is as follows,

var obj = {
a:'aaa', //a is an attribute, 'aaa' is an attribute value
b:' bbb',
c:'ccc'
}

Method one: obj.a// aaa, this method is invalid when for in traverses the object...

Method two: obj['a']//aaa, Quotation marks are required

[The dot method is only suitable when the attribute is a string. If the attribute is a variable, only the latter can be used]

When the attribute is a variable, the value can only be assigned using the following method:

var obj = {};
obj[$a] = 'value';

If you write {$a: 'value'} directly, $a will be parsed into a string.

Three: Usage of keyword in

Format: (variable in object)... Note,,,

When the "object" is an array, the "variable" refers to the "index" of the array;

When "object" is an object, "variable" refers to the "property" of the object.