More difficult. Be prepared in your heart ... Deep breath...
1, For/in:
A method of traversing (enumerating) the properties of an object that can loop through the properties we don't know beforehand.
It can enumerate all of the user-defined attributes, but not some predefined properties and methods.
An attribute that cannot be enumerated is usually an inherited property
To delete an object's properties:
Delete book.width;
The property is removed from the object, and after deletion, the property is not enumerated with for/in and is not detected in the width in book.
Another important use of for/in is to use with associative arrays: (If you forget the definition of associative arrays, you can look at the previous chapters.) ）
For (stoct in port) {
Value + = Get_value (stoct) * PORT[STOCT];
}
2, common object properties and methods:
1): Constructor properties:
Each object has this attribute, and he references the constructor that initializes the object.
Like what:
var d =new Date (); Use the date () constructor to create an object D;
D.constructor ==date; True//attribute d.constructor references Date;
This property helps to determine the type of an object;
Like what:
We want to determine whether the type of a value is a date type:
If ((typeof o== "Object") && (o.constructor==date)) {
First look at the object and see if the date is referenced
}
The above code can also be written as:
If ((typeof o== "Object") && (o instanceof Date)) {
The instanceof operator to detect the value of the O.constructor property.
}
3, Tostirng () and toLocaleString () methods:
1): Tolocalestirng () returns a localized string for the object.
ToString and tolocalestring generally return the same, but in subclasses, there is a difference:
Like what:
Array, date and number define the toLocaleString () method that returns the localized value.
4, hasOwnProperty () and propertyIsEnumerable () methods:
1): hasOwnProperty
var a = {x:1, y:2};
var k =a.hasownproperty ("X");
Alert (k)//true
Alert (Math.hasownproperty ("z"));//false
Alert (Math.hasownproperty ("cos"));//true
Note: Math,cos (): Calculates and returns the cosine of the specified angle in radians.
propertyIsEnumerable () and return results are the same as hasOwnProperty ();
4, isPrototypeOf () method:
If the object to which the method belongs is a prototype object of the parameter.
var a = {x:1, y:2};
var k1= Object.prototype.isPrototypeOf (a); O.constructor = Object
var k2= Object.prototype.isPrototypeOf (Function); Function.constructor = Object
Alert (K1)//true
Alert (K2)//true
5, array:
1 Create an array:
Array Direct Quantity:
var es = [];
Complex dot var es = [[1, {x:1, y:2}], [2, {x:3, y:4}]];
There is another way: Use the Array () constructor:
V1: No parameters:
var a = new Array ();
Empty array, and var a =[] equal;
V2: Multiple parameters:
var a = new Array (1,2,3, "tt"); You can see that the direct quantity definition is simpler.
V3:1 a numeric parameter:
var a = new Array (3);
An array with 3 elements, with a value of undefined for each element;
6, Subscript (index) of the array:
Size: 0 <= Subscript < 2 of 32 times side –1;
If it is not in range, JS will say that it is converted to a string as the name of the object property;
Rather than as the subscript of the array;
Like what:
a[-1.2] = "Test"; Equivalent to a[" -1.2"] = "test";
Code Explanation: Create a property named "1.2" instead of defining a new array element.
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