preface

This chapter introduces new methods for string objects. Don't take important notes for less commonly used methods.
Link to the original text of this chapter: New method of string

includes(),startsWith(),endsWith()

Determines whether one string is contained in another. ES6 provides three new methods.

• The includes() method is used to determine whether one string is contained in another string
• The startsWith() method is used to determine whether the current string starts with another given substring
• The endsWith() method is used to determine whether the current string ends with another given substring

let sampleString = 'Hello world!';

const sample1 = sampleString.includes('llo');
const sample2 = sampleString.startsWith('H');
const sample3 = sampleString.endsWith('d!');
console.log(sample1, sample2, sample3); // true true true

// Use the second parameter
const sample11 = sampleString.includes('llo', 1);
const sample12 = sampleString.startsWith('H', 1);
const sample13 = sampleString.endsWith('d!', 10);
console.log(sample11, sample12, sample13); // true false false

repeat()

The repeat() method returns a new string, indicating that the original string is repeated n times.
If the parameter is decimal, it will be rounded down, and if it is negative and infinite, an error will be reported

const SAMPLE = 'Ha';
let sample1 = SAMPLE.repeat(4); // Repeat four times
console.log(sample1); // HaHaHaHa

let sample2 = SAMPLE.repeat(1.8); // The parameter is a small book, rounded down
console.log(sample2); // Ha

let sample3 = SAMPLE.repeat('3'); // The parameter is a string
console.log(sample3); // HaHaHa

let sample4 = SAMPLE.repeat(-4); // Parameter is negative
console.log(sample4); // Direct error reporting Invalid count value

padStart()，padEnd()

ES2017 introduces the function of string completion length. If a string is not long enough, it will be completed at the head or tail.

• padStart() is used for head completion.
• padEnd() is used for tail completion.

Both padStart() and padEnd() accept two parameters

• Parameter 1: the maximum length of string completion. If the current string is less than the specified length, it is completed.
• Parameter 2: the string used to complete. If the string length is too long, the subsequent extra strings will be deleted. Default space completion.

const SAMPLE = '368';

let newSample = SAMPLE.padStart(11, "000,");
let newSample1 = SAMPLE.padEnd(11, ",000");
console.log(newSample); // 000,000,368
console.log(newSample1); // 368,000,000

trimStart()，trimEnd()

ES2019 adds trimStart() and trimEnd() methods to string instances. The whitespace character of the destination string, whose behavior is consistent with trim(). Whitespace characters include: space, tab, line feed and other whitespace characters.

trim() eliminates whitespace at the beginning and end of a string.
trimStart() eliminates the whitespace in the string header. The alias is: trimLeft();
trimEnd() eliminates whitespace at the end of a string. Alias: trimlight();
The return value is a new string representing the call string with spaces removed.

const SAMPLE = '  Ha  ';
let newSample = SAMPLE.trimStart();
let newSample1 = SAMPLE.trimEnd();
console.log(newSample); // Ha  
console.log(newSample1); //   Ha

matchAll()

The matchAll() method returns a result containing all the matching regular expressions, and returns an iterator.
This is not in-depth, and the regular expression extension will be explained in detail later.

const string = 'sample1sample2sample3';
const regex = /sample/g;

for (const match of string.matchAll(regex)) {
  console.log(match);
}
// Traversal output
/*
['sample', index: 0, input: 'sample1sample2sample3', groups: undefined]
['sample', index: 7, input: 'sample1sample2sample3', groups: undefined]
['sample', index: 14, input: 'sample1sample2sample3', groups: undefined]
*/

replaceAll()

Simply put, you can replace all matches at once.

// grammar
String.prototype.replaceAll(searchValue, replacement);

The replaceAll() method returns a new string. All parts of the new string that meet the pattern have been replaced by replacement

Two parameters

• Parameter 1: it can be a string or a global regular expression (with g modifier).

• Parameter 2: the second parameter replacement is a string, which represents the replaced text. Some special strings can be used. In addition to being a string, it can also be a function whose return value will replace the text matching the first parameter searchValue.

  • $&: matching string.
  • $`: matches the text in front of the result.
  • $': matches the text after the result.
  • $n: the nth group of content matched successfully. N is a natural number starting from 1. The precondition for this parameter to take effect is that the first parameter must be a regular expression.
  • $$: refers to the dollar sign $.

const SAMPLE = 'HaHa，huhu，hehe';
let sample1 = SAMPLE.replaceAll('h', 'H');
let sample2 = SAMPLE.replaceAll('H', () => 'h');
console.log(sample1); // HaHa，HuHu，HeHe
console.log(sample2); // haha，huhu，hehe

String.raw()

ES6 also provides a raw() method for native String objects. Is used to obtain the original String of a template String. In most cases, String.raw() is used to process template strings.

console.log(`Hi\n${2+3}!`); // 
/*
output
Hi
5!
*/
console.log( String.raw`Hi\n${2+3}!`); // Output Hi\n5!

String.fromCodePoint()

The String.fromCodePoint() static method returns a string created using the specified sequence of code points. It can recognize characters larger than 0xFFFF, which makes up for the deficiency of String.fromCharCode() method.

console.log(String.fromCodePoint(9731, 9733, 9842, 0x2F804));
// Direct output ☃ ★ you