JavaScript Object properties and array access

Access to JavaScript Object properties
If there is an object test:
var test = {
"A": 1,
"B": 2
};
There are two ways to directly access the value of the property A of the object test:

1.TEST.A;

2.test["a"]; (Note that the quotation marks are used here.)



However, if you use the For/in statement to access the object's property values, you must use the "[]" operator:
For (m in test) {
Alert (test[m]);
alert (TEST.M); The undefined will pop up here.
}
Why pinch? Because the For/in loop assigns the object's property name as a string to the variable m.



The array of JavaScript is nothing more than a special object, so:
var arr = new Array ();
Arr[0] = 10;
Arr[' a '] = 20;

For (m in arr) {
Alert (m); Eject 0 and a
Alert (arr[m]); Eject 10 and 20
}

JavaScript Object properties and array access