Collection of js common code snippets_javascript skills

Each piece of code is preceded by explanatory text such as functional annotations and parameter requirements. It is not difficult, so no more comments are made. In order to see clearly, here is a small directory in order:
Rewrite window.setTimeout,
Understand the return pattern of recursive programs,
Intercept long strings,
Get the element's position on the page Absolute position,
statistics, removal of duplicate characters (implemented by multiple methods),
random shuffling of ordered array elements (implemented by multiple methods).

Copy code The code is as follows:

/*
Function: Modify window.setTimeout so that it can pass parameters and object parameters (can also be used for setInterval)
Usage method: setTimeout(callback function, time, parameter 1,... ., parameter n) (FF has native support, IE does not support)
*/
var __sto = setTimeout;
window.setTimeout = function(callback,timeout,param){
var args = Array.prototype.slice.call(arguments,2);
var _cb = function(){
callback.apply(null,args);
}
__sto(_cb,timeout);
}
function aaaaa(a,b,c){
alert(a b c);
}
window.setTimeout(aaaaa,2000,5,6,7);

/**//*
Function: Understand the return pattern of recursive programs (from inside to outside)
Mutual references of members between objects
*/
var ninja = {
yell: function(n){
return n > 0 ? ninja.yell(n-1) "a" : "hiy ";
}
};
alert(ninja.yell(4))//The result is: hiyaaaa;
var samurai = { yell: ninja.yell };
//var ninja = {}; // Whether the comment here affects the result
try {
alert(samurai.yell(4));
} catch(e){
alert("Uh , this isn't good! Where'd ninja.yell go?" );
}

/**Function: intercept long string
* @param {string} str String to be intercepted
* @param {number} size interception length (single byte length)
*/
var subStr = function(str, size){
var curSize = 0, arr = [];
for(var i = 0, len = str.length; i < len; i ){
arr.push(str.charAt(i)) ;
if (str.charCodeAt(i) > 255){
curSize = 2;
if(size === curSize || size === curSize - 1){
return arr .join('');
}
}else{
curSize ;
if(size === curSize){
return arr.join('');
}
}
}
};
var str = '#%*...What 1234abcd is not long enough';
alert(str.length);
alert( str.substr(0, 15));
alert(subStr(str, 15));

/**//*
Function: Get the absolute position of the element on the page (relative to the upper left corner of the page)
@param {string} node DOM element whose position is to be sought
*/
function getAbsPosition(node) {
var t = node.offsetTop;
var l = node.offsetLeft;
while (node ​​= node.offsetParent) {
t = node.offsetTop;
l = node.offsetLeft;
}
alert("top=" t "n" "left=" l);
}

/**//*
Function: Statistics, removal of repeated characters
@param str String to be counted
Description: Commonly used to count repeated characters in strings, or repeated letters, numbers, etc. in arrays.
Here are two typical types collected from the Internet, each with two implementation methods. There are many other variants, written from different angles, and can be searched and learned.
The data to be counted can be either an array or a string. Just use String.split() or Array.join()
to convert it into the type required by the function parameters.
*/
// Type 1: Use new objects to Save data
var count1 = function (str) {
var map = {}, maxCount = 0, maxChar, undefined, i = str.length;
while (i--) {
var t = str.charAt(i);
map[t] == ​​undefined ? map[t] = 1 : map[t] = 1;
if (map[t] > maxCount) {
maxChar = t;
maxCount = map[maxChar];
}
}
return "Character:" maxChar "Number of times:" maxCount;
}
function s_0(a) { // The parameters here should be array type
var b = {}, c = [], i;
for (i = 0; i < a.length; i ){
if ( !b[a[i]]) {
c[c.length] = a[i], b[a[i]] = true;
}
}
return c;
}
// Type 2: Regular expression matching statistics
var count2 = function (str) {
var most = str.split('').sort().join('') .match(/(.)1*/g); //Arrange repeated characters
most = most.sort(function (a, b) { return a.length - b.length }).pop(); / /Sort by frequency
return most.length ': ' most[0];
}
function s_1(a) {
var a = a.join(""), b = [ ];
while (a.length > 0)
a = a.replace(new RegExp((b[b.length] = a.charAt(0)), "g"), "") ;
return b;
}

/**//*
Function: Disorganize an ordered array (generate an unordered random array)
Description: Basic sorting algorithm Everyone should be very clear. However, the opposite operation is often used in programming, that is, randomly shuffling the original ordered array elements.
The following are three methods. The first one was written by myself before. Due to the poor level, the time complexity of the code I wrote was too high.
So I searched for some simple and efficient methods from the Internet. .
The second is said to be the "shuffling algorithm", which many people must have heard of;
The third is to use the built-in sort method of JS, which is very simple to implement.
*/
// Method 1 (to teach everyone the lessons of failure)
function randArray(num) {
var rands = [];
var ra = parseInt(num * Math .random());
rands.push(ra);
for (var r = 0; r < num - 1; r ) {
ra = parseInt(num * Math.random() );
for (var m = 0; m < rands.length; m ) {
while (rands[m] == ra) {
ra = parseInt(num * Math.random() );
m = -1;
}
}
rands.push(ra);
}
//alert(rands);
return rands;
}
//Method 2:
//Select a random number between two [0...array.Length), and exchange the two subscripted elements (this is more efficient in ordering)
/* Note: This is a "shuffling algorithm". Someone has proved that the effect of shuffling is as follows:
The effect of randomly exchanging nums/2 times is very poor. On average, about 1/3 of the objects are still in their original positions
It is basically usable after randomly exchanging nums times, and on average about 15% of the objects are still in the original position
It is really usable after randomly exchanging nums*2 times, and about 2% of the objects are still in the original position on average
*/
function daluan(nums) {
var array=[];
for (var i = 0; i < nums; i ) {
array[i] = i;
}
for (var i = 0; i < nums; i ) {
var rand = parseInt(nums * Math.random());
var temp = array[i];
array[ i] = array[rand];
array[rand] = temp;
}
return array;
}
// Method 3:
// Let the comparison function pass randomly Just return -1 or 1 (the reordering efficiency may not be high)
var testArray3=[1,2,3,4,5,6,7,8,9,10,22,33,55, 77,88,99];
testArray3.sort(function(){return Math.random()>0.5?-1:1;});
alert(testArray3);