Common JavaScript Tips

• Convert string to Numeric

General Method:

var var1 = parseint ("2"), var var2 = parsefloat ("2"), var var3 = number ("2"), var var3 = new Number ("2");

Simple method:

var var1 = + ("2");

• Converting other types to Boolean types

In JavaScript, all values can be implicitly converted to a Boolean type:

Data type	The value converted to true	Value converted to False
Boolean	True	False
String	Any non-empty string	"" (empty string)
Number	Any non-0 numeric value (including infinity)	0, NaN
Object	Any object	Null
Undefined	(Not applicable)	Undefined

Example:

0 = = false; True1 = = true; True ' = = false//Truenull = = false//True

We can also display the conversion to a Boolean type:

var a = Boolean ("Hello"); True

A simpler approach:

var a = "Hello"; var b =!! A

• Creating multidimensional arrays

General Method:

var arr = new Array (2); arr[0] = new Array (2); arr[1] = new Array (2); arr[0][0] = 1;arr[0][1] = 2;arr[1][0] = 3;arr[1][1] = 4 ;

Simple method:

var arr = {};arr[[0, 0]] = 1;arr[[0, 1]] = 2;arr[[1, 0]] = 3;arr[[1, 1]] = 4;

• Prevent others from loading your page in an IFRAME

Prevent your Web page from embedding its own web pages through an iframe:

if (top!== window) {   top.location.href = window.location.href;}

This code should be placed in the head of each page.

• Convert an arguments parameter object to an array

In JavaScript, the predefined variable arguments in a function is not a true array, but an array-like object. It has the length property, but there are no slice, push, sort functions for the array object, and these are sometimes used in functions, so we need to convert the arguments to a real array:

function func () {    var arr = Array.prototype.slice.call (arguments, 0);    return arr;}

• Traverse the resulting regular result

General Method:

var str = "132ada5d6g3j"; var match = Str.match (/\d/g, str); var arr = [];var j;for (var i = 0, j = match.length; I < J; I + +) {    Arr.push (match[i]);} Console.log (arr);

Quick Method:

var str = "132ada5d6g3j"; var arr = []; Str.replace (/\d/g, function () {    arr.push (arguments[0]);}); Console.log (arr);

Another quick way:

var str = "132ada5d6g3j"; var arr = str.replace (/\d/g, "). Split ('); Console.log (arr);

• Get the maximum value in a numeric array

General Method:

var arr = [1, 5, 4, 12355, 123, 123, 3, 4454, 43];var max = Arr[0];for (var i in arr) {    if (Arr[i] > max) {        m AX = arr[i];}    } The/* Loop may also be: for (var i = 0, j = arr.length; I < J; i++) {    if (Arr[i] > max) {        max = arr[i];}    } */console.log (max);

Simple method:

var arr = [1, 5, 4, 12355, 123, 123, 3, 4454, 43];var max = Math.max.apply (null, arr); Console.log (max);

• Digital rounding

General Method:

var num = 5.63;console.log (Math.floor (num));

Other Method 1 (only available for numbers not less than 0):

var num = 5.63;console.log (num>>>0);

Other Method 2 (positive negative numbers are available, recommended):

var num = 5.63;console.log (~~num);

• Fix An error similar to 0.1+0.2! = 0.3

In JavaScript, numbers are based on IEEE754 values, so there is a case of floating-point arithmetic errors, which is a common problem with IEEE754, not the language itself:

var num = 0.1 + 0.2; 0.30000000000000004console.log (num = = 0.3); False

Correction Method:

var num = 0.1 + 0.2; 0.30000000000000004console.log (num);/* You can specify the number of decimal digits rounded by the ToFixed method: */console.log (Num.tofixed ()); "0" Console.log (num.tofixed (1)); "0.3"

• Integer pre-complement 0

Common methods:

/* Note that the n here indicates the number of digits after Num 0 is */function addzero (num, n) {  var len = num.tostring (). length;  while (Len < n) {    num = "0" + num;    len++;  }  return num;} Console.log (Addzero (5,8)); 00000005

Simple method:

function Addzero (num, n) {   y= ' 00000000000000000000000000000 ' +num;/* Here 0 of the number can be adjusted *   /return Y.substr (Y.LENGTH-N) ;} Console.log (Addzero (5,8)); 00000005

——————————————————————-

The performance issues of string connections should be classic, not detailed.

Article Source: http://i.cnblogs.com/EditPosts.aspx?opt=1