【JavaScript】String 例項方法（二）

阿新 • • 發佈：2020-08-28

以下內容為學習記錄，可以參考 MDN 原文。

環境

node v12.18.1
npm 6.14.5
vscode 1.46
Microsoft Edge 83

normalize

normalize() 方法會按照指定的一種 Unicode 正規形式將當前字串正規化。（如果該值不是字串，則首先將其轉換為一個字串）。

const name1 = '\u0041\u006d\u00e9\u006c\u0069\u0065';
const name2 = '\u0041\u006d\u0065\u0301\u006c\u0069\u0065';

console.log(`${name1}, ${name2}`);
// expected output: "Amélie, Amélie"
console.log(name1 === name2);
// expected output: false
console.log(name1.length === name2.length);
// expected output: false

const name1NFC = name1.normalize('NFC');
const name2NFC = name2.normalize('NFC');

console.log(`${name1NFC}, ${name2NFC}`);
// expected output: "Amélie, Amélie"
console.log(name1NFC === name2NFC);
// expected output: true
console.log(name1NFC.length === name2NFC.length);
// expected output: true

padEnd

padEnd() 方法會用一個字串填充當前字串（如果需要的話則重複填充），返回填充後達到指定長度的字串。從當前字串的末尾（右側）開始填充。

const str1 = 'Breaded Mushrooms';

console.log(str1.padEnd(25, '.'));
// expected output: "Breaded Mushrooms........"

const str2 = '200';

console.log(str2.padEnd(5));
// expected output: "200  "

padStart

padStart() 方法用另一個字串填充當前字串(重複，如果需要的話)，以便產生的字串達到給定的長度。填充從當前字串的開始(左側)應用的。

const str1 = '5';

console.log(str1.padStart(2, '0'));
// expected output: "05"

const fullNumber = '2034399002125581';
const last4Digits = fullNumber.slice(-4);
const maskedNumber = last4Digits.padStart(fullNumber.length, '*');

console.log(maskedNumber);
// expected output: "************5581"

repeat

repeat() 構造並返回一個新字串，該字串包含被連線在一起的指定數量的字串的副本。

const chorus = 'Because I\'m happy. ';

console.log(`Chorus lyrics for "Happy": ${chorus.repeat(27)}`);

// expected output: "Chorus lyrics for "Happy": Because I'm happy. Because I'm happy. Because I'm happy. Because I'm happy. Because I'm happy. Because I'm happy. Because I'm happy. Because I'm happy. Because I'm happy. Because I'm happy. Because I'm happy. Because I'm happy. Because I'm happy. Because I'm happy. Because I'm happy. Because I'm happy. Because I'm happy. Because I'm happy. Because I'm happy. Because I'm happy. Because I'm happy. Because I'm happy. Because I'm happy. Because I'm happy. Because I'm happy. Because I'm happy. Because I'm happy. "

replace

replace() 方法返回一個由替換值（replacement）替換一些或所有匹配的模式（pattern）後的新字串。模式可以是一個字串或者一個正則表示式，替換值可以是一個字串或者一個每次匹配都要呼叫的回撥函式。

const p = 'The quick brown fox jumps over the lazy dog. If the dog reacted, was it really lazy?';

const regex = /dog/gi;

console.log(p.replace(regex, 'ferret'));
// expected output: "The quick brown fox jumps over the lazy ferret. If the ferret reacted, was it really lazy?"

console.log(p.replace('dog', 'monkey'));
// expected output: "The quick brown fox jumps over the lazy monkey. If the dog reacted, was it really lazy?"

search

search() 方法執行正則表示式和 String 物件之間的一個搜尋匹配。

const paragraph = 'The quick brown fox jumps over the lazy dog. If the dog barked, was it really lazy?';

// any character that is not a word character or whitespace
const regex = /[^\w\s]/g;

console.log(paragraph.search(regex));
// expected output: 43

console.log(paragraph[paragraph.search(regex)]);
// expected output: "."

replaceAll

replaceAll() 方法返回一個新字串，該字串的所有模式匹配均由替換替換。模式可以是字串或 RegExp，而替換項可以是字串或每個匹配項要呼叫的函式。

const p = 'The quick brown fox jumps over the lazy dog. If the dog reacted, was it really lazy?';

const regex = /dog/gi;

console.log(p.replaceAll(regex, 'ferret'));
// expected output: "The quick brown fox jumps over the lazy ferret. If the ferret reacted, was it really lazy?"

console.log(p.replaceAll('dog', 'monkey'));
// expected output: "The quick brown fox jumps over the lazy monkey. If the monkey reacted, was it really lazy?"

slice

slice() 方法提取某個字串的一部分，並返回一個新的字串，且不會改動原字串。

const str = 'The quick brown fox jumps over the lazy dog.';

console.log(str.slice(31));
// expected output: "the lazy dog."

console.log(str.slice(4, 19));
// expected output: "quick brown fox"

console.log(str.slice(-4));
// expected output: "dog."

console.log(str.slice(-9, -5));
// expected output: "lazy"

split

split() 方法使用指定的分隔符字串將一個 String 物件分割成子字串陣列，以一個指定的分割字串來決定每個拆分的位置。

const str = 'The quick brown fox jumps over the lazy dog.';

const words = str.split(' ');
console.log(words[3]);
// expected output: "fox"

const chars = str.split('');
console.log(chars[8]);
// expected output: "k"

const strCopy = str.split();
console.log(strCopy);
// expected output: Array ["The quick brown fox jumps over the lazy dog."]

startsWith

startsWith() 方法用來判斷當前字串是否以另外一個給定的子字串開頭，並根據判斷結果返回 true 或 false。

const str1 = 'Saturday night plans';

console.log(str1.startsWith('Sat'));
// expected output: true

console.log(str1.startsWith('Sat', 3));
// expected output: false