JS operator, control flow, circulation, the string / array Method

Operators

• Arithmetic operators: +, -, *, /,%, +, -
• Assignment operator: =, + =, - =, * =, / =,% =
• Comparison operators:>,> =, <, <=, =, ==, === (congruent, also to compare data type)!
• Logical operators: && (and), || (or),! (Non)
  
  

Process Control

• In making this judgment, when the following is false
  • 0
  • null
  • undefined
  • NaN
  • "" Empty string
  • false
• if else

if (...) {
    ...
} else if(...) {
    ...
} else {
    ...
}
// 三目运算符
name ? console.log("存在："+name) :console.log("不存在")
//多条件下的三目运算符
0 ? console.log(1) : 3>4 ? console.log(2) : console.log(3)

• switch

var choice = 1;
switch (choice) {
    case 1:
        document.write(1);
        //不写break时，当满足条件是，不再判断，会执行后面所有语句
        break;
    case 2:
        document.write(2);
        break;
    default:
        document.write("都不满足");
}

cycle

• for loop

//九九乘法表
for (i=1; i<=9; i++){
    for(j=1; j<=i; j++){
        document.write(j+"*"+i+"="+i*j+'&emsp;');
    }
    document.write("<br>");
}

• while loop

while (true){
    document.write(1);
    break;
}

• do while loop

do{
    document.write(1);
}while (1<0)

String Methods

• Length: length
• Index: [] / charAt ()
• Replace: replace ()
• Split: split ()
• Uppercase: toUpperCase ()
• Lowercase: toLowerCase ()
• Index: indexOf ()
• Interception: substring ()
• Cutting: slice ()

var str_test = "Which Love Love";
document.write(str_test.length+'<br>');//length
document.write(str_test[0]+'<br>');//[]
document.write(str_test.charAt(1)+'<br>');//charAt()
document.write(str_test.replace("Love","===")+'<br>');//replace()
document.write(str_test.split(' ')+'<br>');//split()
document.write(str_test.toUpperCase()+'<br>');//toUpperCase()
document.write(str_test.toLowerCase()+'<br>');//toLowerCase()
document.write(str_test.indexOf('L',8)+'<br>');//indexOf()
//slice()不会自动比较参数的大小
document.write(str_test.slice(0,5)+'<br>');//slice()
//substring()会自动比较参数的大小
document.write(str_test.substring(5,0)+'<br>');//substring()

Array Methods

• Length: length
• Index: []
• Additional: push ()
• Add: unshift ()
• After deletion: pop ()
• Before deletion: shift ()
• Index: indexOf ()
• Slice: slice ()
• Replace: splice ()
• Stitching: join ()
• Sort: sort ()
• Reverse: reverse ()
• Connection: concat ()

var arr = ['one','two','three','four','five'];
document.write(arr.length+'<br>');//length
document.write(arr[0]+'<br>');//[]
arr.push('six');//push()
arr.unshift('zero');//Unshift()，从前面添加
arr.pop();//pop()
arr.shift();//shift()
document.write(arr.indexOf('two')+'<br>');//indexOf()
document.write(arr.slice(0,3)+'<br>');//slice()
//将新的值，替换从下标为1的开始的两个值
document.write(arr.splice(1,2,'a','b','c','d')+'<br>');//splice()
document.write(arr.join('==')+'<br>');//join()
document.write(arr.sort()+'<br>');//sort()
document.write(arr.reverse()+'<br>');//reverse()
var arr_temp1=[1,2];
var arr_temp2=[3,4];
document.write(arr.concat(arr_temp2,arr_temp1)+'<br>');//concat()

Other methods

• Into a string: toString ()
• Rounds: toFixed ()
• Judgment NaN: isNaN ()
• Analyzing array: Array.isArray ()
• Integer: parseInt ()
• Float: parseFlost ()
• Digital: Number ()

var num = 12.8;
var a ='0x1234';
var b ='343.324';
document.write(typeof toString(num)+'<br>');//toString()
document.write(num.toFixed()+'<br>');//toFixed()
document.write(isNaN(num)+'<br>');//isNaN()
document.write(Array.isArray(num)+'<br>');//isArray()
document.write(parseInt(a)+'<br>');//parseInt()
document.write(parseFloat(b)+'<br>');//parseFloat()
document.write(Number(b)+'<br>');//Number()