Web front-end --JavaScript notes

js

type of data

The string can be '' or ''

Operators

• == Only relatively content
• === Comparison of content, but also more type is the same, only two are true is true
• !==And above ===contrary

var a=123;
var b="123";
//a==b 结果为true
//a===b 结果为false
//a!==b 结果为true

variable

js the variables are global, local variables the same name will also change the original data

var i=2;
for(var i=0;i<5;i++){
    console.log('hello');
}
console.log(i);//这里的i等于4

let Keywords local variable, does not modify the global variable

var i=2;
for(let i=0;i<5;i++){
    console.log('hello');
}
console.log(i);//这里的i等于2

method

js compiled from top to bottom, however, if the method is in the back, he can perform the method, the compiler even if no method of

//console.log(hello); 打印函数内容
//console.log(hello()); 打印函数内容，之后执行函数
hello();
function hello(){
    console.log("hello world!");
}

Method returns without return type defined in the foregoing method

function print(){
    return "";
}

other

• querrySelector

  querrySelector is in jQuery method
  querrySelector ( "# mydiv p") getElementById compared with other methods, more flexible, allowing a hierarchical relationship
  • querrySelector ( "# mydiv") id selector
  • querrySelector ( "div") tag selector (only get the first div tag)
  • querrySelector ( ". mydiv") class selector
• innerHtml If there is text html, which can recognize text html tags

• innerText Only into the text, which does not recognize the tag

The body tag onload equivalent windows.onload

• es6 (JavaScript1.6) string concatenation

//es6中，year和month是变量 换行直接换，不需要“+”
var str = `${year}年${month}月`；
//会保留空格以及换行
var str = `${year}年
            ${month}月`

• Analyzing element is empty es6

var e = document.getElementById("h");
//e存在为true，不存在则为false
if(e){
    
}

• es6 array traversal

var array1 = ["a","b","c"];
array1.foreach(function(element){
    console.log(element);
});