ES6 new API: String (1)

1. String.raw

   String.raw is a label function template string (if you do not know what label function, point ⚑), which returns the template string of original string . For example, \n will not be treated as a newline, but will be treated as two ordinary characters \ and n :

   console.log(String.raw`1\n2`); //1\n2

Usually, we don't need to call it as a normal function, but if you must call it as a normal function, pay attention to the format of the incoming parameters:

(template: {
    raw: readonly string[] | ArrayLike<string>;
}, ...substitutions: any[])=>string

String.raw first argument must be a raw object attributes, the attribute value character array or character class array , the value of remaining parameters is inserted.

console.log(String.raw({ raw: 'abcd' }, 0, 1, 2)); //a0b1c2d
//3 4两个插值超出了模板数组的范围，会被忽略
console.log(String.raw({ raw: ['a', 'b', 'c', 'd'] }, 0, 1, 2, 3, 4)); //a0b1c2d

2. String.prototype.repeat

   Function type:

   (count?:number)=>string

repeat function according to the parameters passed n , a return to the original string repeated n times new string , parameters n default 0 .

//传入0或者不传参数时，原字符串重复0次，返回空字符串
console.log('a'.repeat(0));// ''
console.log('a'.repeat(2));// 'aa'

3. String.prototype.startsWith,String.prototype.endsWith,String.prototype.includes

   Function type:

   (queryString?:string,startPosition?:number)=>boolean

startsWith , endsWidth and includes functions are new functions for checking strings in ES6. They receive two parameters. The first parameter queryString is the string to be queried in the original string, and the second parameter startPostion is the start query s position. In includes and startsWith , startPosition defaults to 0 , in endsWith , startPostion defaults to original string length .

console.log('abcde'.includes('a')); //true
//改变起始位置
console.log('abcde'.includes('a', 1)); //false
console.log('abcde'.startsWith('a')); //true
//改变起始位置
console.log('abcde'.startsWith('a', 1)); //false

console.log('abcde'.endsWith('a')); //false
//改变起始位置
console.log('abcde'.endsWith('a', 1)); //true

It should be noted that when the string to be checked, that is, the parameter queryString is empty string '' , the return result of these three functions is always true .

console.log('abcde'.includes('')); //true
//改变起始位置
console.log('abcde'.includes('', 1)); //true
console.log('abcde'.startsWith('')); //true
//改变起始位置
console.log('abcde'.startsWith('', 1)); //true
console.log('abcde'.endsWith('')); //true
//改变起始位置
console.log('abcde'.endsWith('', 1)); //true