Introducing several encapsulation functions in javascript-ecma

First introduce the following methods:

String method:

str.length str.charAt(i): Get a certain value in the string a;

str.indexOf('e'); Find the first occurrence; if not found, return -1;

str.lastIndexOf('e'): Find the last one The position where e appears; cannot be found and returns -1;

str.toUpperCase(); Convert to uppercase str.toLowerCase(); Convert to lowercase str.substring (starting position, ending position): characters String interception; str.split('cutting method'); string cutting; string conversionarray;

array method:
Delete: arr.splice (starting position, number of deleted items); Add: arr.splice (starting position [which bit to add in front], 0, element 1····); Replacement: arr.splice (starting position, number of deleted items, element 1···); arr.sort(function(n1,n2){return n1 - n2}): sort arr.reverse(): flip arr.push (); add one digit to the back of the array; arr.unshift(): add one digit to the front of the array; arr.pop(): delete one digit from the back of the array; arr.shift(): delete one digit from the front of the array ; arr.join('Connection method'); Method of converting array to string; arr.concat(arr1, arr2····); Array connection;

Mathematical method:

Math.random(); Random number; Math.round(): Rounding; Math.ceil() Rounding up; Math.floor() Rounding down; Math.abs() : Take the absolute value; Math.max(x,y): Find the maximum number; Math.min(x,y); Find the minimum number; Math.pow(x,y): How many powers of a number; Math.sqrt( ): square root;

Array: store multiple things; json: store multiple things; json = { //Key-value pairs name1[key,key]:value1[value,value], name2[key ,key]:value2[value,value], }

The difference between json and arr:

1: length undefined arr.length;

2: Subscript attribute method arr[0];

3: Order No order With order;

4: Loop for in for,while,for in

for The in loop can also loop through arrays, but it is not recommended because the performance is slightly lower;

JS small features: comma expression: only look at the value after the last comma;

The following is a small function that obtains element encapsulation through class:

//getByClass(oParent,sClass);//oParent:从哪个父级下面获取;sClass:要获取的是哪个class名字;
function getByClass(oParent,sClass){
    if(oParent.getElementsByClassName){
        return oParent.getElementsByClassName(sClass);
    }else{
        var aEle = oParent.getElementsByTagName('*');
        var arr = [];
        for(var i = 0; i < aEle.length; i++){
            var tmp = aEle[i].className.split(&#39; &#39;);
            if(findInArr(sClass,tmp) == true){
                arr.push(aEle[i]); 
            }
        }
        return arr;
    }
}　

Here are a few more small cases:

1. How many days are there in this month

<script>
        var oDate=new Date();
        oDate.setMonth(oDate.getMonth()+1);
        oDate.setDate(0);
        alert(oDate.getDate())
</script>

2. What day of the week is the first day of this month

<script>
   var oDate=new Date();
   oDate.setDate(1);
   alert(oDate.getDay());
</script>

3. Multiplication table

<script>
    document.write(&#39;<table>&#39;);
    for(var i = 1; i <= 9; i++){
        document.write(&#39;<tr>&#39;);
        for(var j = 1; j <= i; j++){
            document.write(&#39;<td>&#39;+i+&#39;*&#39;+j+&#39;=&#39;+i*j+&#39;</td>&#39;);
        }
        document.write(&#39;</tr>&#39;);
    }
    document.write(&#39;</table>&#39;);
</script>

4. Convert json to string

<script>
    var json={a:12,b:5,c:9,d:6};
    var arr=[];
    for(var name in json){
        arr.push(name+&#39;=&#39;+json[name])
    };
    //alert(arr);
    var str=arr.join(&#39;&&#39;);
    alert(str);
</script>

【Related recommendations】

1. Free js online video tutorial

2. JavaScript Chinese Reference Manual

3. php.cn Dugu Jiujian (3) - JavaScript video tutorial

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