Collection of basic knowledge of javascript (2) Recommended collection_Basic knowledge

/**
* Find substrings that meet the requirements in the source string.
* @return {}
*/
function MatchDemo() {
var r, re; // Declare variables.
var s = "The rain in Spain falls mainly in the plain";
re = new RegExp("ain", "g"); // Create a regular expression object.
r = s.match(re); // Find a match in string s.
return (r);
}

/**
* Returns all string and position information in the source string that satisfies the regular expression.
*/
function RegExpTest() {
var ver = Number(ScriptEngineMajorVersion() "."
ScriptEngineMinorVersion())
var ans = '';
if (ver >= 5.5) { // Test the JScript version.
var src = "The rain in Spain falls mainly in the plain.";
var re = /w /g; // Create a regular expression pattern.
var arr;
while ((arr = re.exec(src)) != null)
ans = arr.index "-" arr.lastIndex arr "t";
} else {
ans = "Please use an updated version of JScript";
}
return ans;
}

/**
* Perform a regular expression check on the source string to see if it conforms to the regular expression.
*/
function TestDemo() {
var s1;
var source = "abcdefg";
var regex = /w /g; // Create a regular expression pattern.
if (regex.test(source))
s1 = " contains ";
else
s1 = " does not contain ";
return ("'" source "'" s1 " '" regex.source "'");
}

/**
* Find the regular expression string in the source string.
* @return {}
*/
function SearchDemo() {
var r, re;
var s = "The rain in Spain falls mainly in the plain.";
re = /falls/i;
r = s.search(re);
return (r);
}

function add (a,b)
{
alert(a b);
}
function sub(a,b)
{
alert(a-b);
}

add.call(sub,3,1);
//The meaning in this example is to replace sub with add, add.call(sub,3,1) == add(3,1), So the running result is: alert(4);

function Class1()
{
this.name = "class1";

this.showNam = function()
{
alert(this.name);
}
}

function Class2()
{
this.name = "class2";
}

var c1 = new Class1();
var c2 = new Class2();

c1.showNam.call(c2);
//call means to put the method of c1 in Executed on c2. It turns out that c2 does not have a showNam() method. Now the showNam() method of c1 is put on c2 for execution, so this.name should be class2, and the execution result is: alert ("class2");

function Class10()
{
this.showSub = function(a,b)
{
alert(a-b);
}
}

function Class11()
{
this.showAdd = function(a,b)
{
alert(a b);
}
}


function Class2()
{
Class10.call(this);
Class11.call(this);
}

function Person(name,age){ //Define a class, human
this.name=name; //Name
this.age=age; //Age
this.sayhello=function(){alert ("hello")};
}
function Print(){ //Display class attributes
this.funcName="Print";
this.show=function(){
var msg=[];
for(var key in this){
if(typeof(this[key])!="function"){
msg.push([key,":", this[key]].join(""));
}
}
alert(msg.join(" "));
};
}
function Student( name,age,grade,school){ //Student class
Person.apply(this,arguments);
Print.apply(this,arguments);
this.grade=grade; //Grade
this.school=school; //school
}
var p1=new Person("jake",10);
p1.sayhello();
var s1=new Student(" tom",13,6,"Tsinghua Primary School");
s1.show();
s1.sayhello();
alert(s1.funcName);

Math.max can be followed by any number of parameters, and finally the maximum value among all parameters is returned.

For example
alert(Math.max(5,8)) //8
alert(Math.max(5,7,9,3,1,6)) //9

But in many cases, we need to find the largest element in an array.
var arr=[5,7,9,1]
alert(Math.max(arr)) // This doesn’t work. Be sure to write it like this

function getMax(arr){
var arrLen=arr.length;
for(var i=0,ret=arr[0];iret=Math.max(ret,arr[i]);
}
return ret;
}

To use apply, look at the code:
function getMax2( arr){
return Math.max.apply(null,arr);
}

Another example is the push method of an array.
var arr1=[1,3,4];
var arr2=[3,4,5];
If we want to expand arr2, then append to arr1 one by one, and finally let arr1 =[1,3,4,3,4,5]
arr1.push(arr2) obviously does not work. Because doing this will get [1,3,4,[3,4,5]]

We can only use a loop to push one by one (of course you can also use arr1.concat(arr2), but The concat method does not change arr1 itself)
var arrLen=arr2.length
for(var i=0;iarr1.push(arr2[i]);
}

Array.prototype.push.apply(arr1,arr2)