> For the complete documentation index, see [llms.txt](https://hannahpun.gitbook.io/leetcode-note/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hannahpun.gitbook.io/leetcode-note/tools/string-method.md).
# String Method
## Method Table
| Method | return | example |
| ----------------------------------------------- | -------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| trim() | 沒有多餘空格的 “字串” (只會移掉兩端空白) | " s".trim(); // "s" |
| **Capture some words** | | |
| indexOf(searchValue\[, fromIndex]) | 搜尋字串(searchValue) 所在的 “位置 (Number)”
第二個參數 fromIndex 可以指定從哪個位置開始搜尋，若找不到會回傳 -1
| 'Blue'.indexOf('blue'); // -1 |
| charAt(index) | 位置(index) 所在的 “字串”，若找不到會回傳 ” 空字串 | 'Brave new world'.charAt(4) // e |
| substr(start\[, length]) | 從 start 這個位置開始，總長 length 的 “字串”．若 length 沒有值則等於等於從 start 到字串最後一個字都抓出來 | 'abcdefghij'.substr(1, 2) // bc |
| substring(indexStart, indexEnd) | 從 start 這個位置開始，到不包含 end 的字串 | 'abcdefghij'.substring(1, 2) // b |
| **Find something** | | |
| startsWith(str) | 看是否為 str 開頭 | "hannah".startsWith("ha") // true |
| match(regex) | 符合 regex 條件的 “Array”，若沒有丟參數進去 Array\[0] 會是 “” 空字串，若參數 regex 都不符合會回傳 null | "hannah1".match(/\d/i);
// \[1, index: 6, input: 'hannah1'...]
|
| search(regex) | 符合 regex 條件並第一個找到的 Number，若找不到就會回傳 -1 | "hey JudE".search(/\[A-Z]/g) // 4 |
| replace(regexp\|substr, newSubstr\|function) | 原本字串用 regex 或 substr 搜尋，找到符合條件就用 newSubstr 取代成為新字串 | var str = 'Twas the night before Xmas...';
str.replace(/xmas/i, 'Christmas');
var str = 'Twas the night'
str.replace(/the/i, (match) => "123");
// Twas 123 night
|
| replaceAll(regexp\|substr, newSubstr\|function) | 取代多個 | var str = "minusminusplusplus";
str.replaceAll('minus', "-"); // "--plusplus"
|
| | | |
| slice(beginIndex\[, endIndex]) | 切過的新字串(包含 beginIndex 不含 endIndex) | |
| split(\[separator\[, limit]]) | (拆開) 回傳經過 separator 拆開的 Array，可以搭配使用 Array.join() 組合成不一樣的字串 (也可以用 regex) | "hi hana".split(" ");
// \['hi', 'hana']
split(/\[^a-z]/)
// split 不是 alpha 的
"/.../a/../b/c/../d/./"
-> \['', '...', 'a', '..', 'b', 'c', '..', 'd', '.', '']
|
| includes(searchString\[, position]) | Boolean | 'To be, or'.includes('To be') // true |
| charCodeAt(index) | 將英文字母轉為 ASCII Code | 'Aao'.charCodeAt(1) // a 是 97 |
| String.fromCharCode(Number\[, Number]) | 將數值轉換成回字串 | String.fromCharCode(65, 97, 111) // Aao |
### Match(regex)
```
// 1
"hannah1".match(/\d/i)
// 2
let regex1 = new RegExp(/\d/, "i")
"hannah1".match(regex1)
```
### [Replace multiple strings with multiple other strings](https://stackoverflow.com/questions/15604140/replace-multiple-strings-with-multiple-other-strings)
```javascript
var str = "minusminusplusplus"; // need convert to "--++"
let mapObj = {
"minus": "-",
"plus": "+"
}
str.replace(/minus|plus/gi, function(matched){
return mapObj[matched];
});
```
### Replace(egexp|substr, newSubstr|function)
原來 replace 也是可以帶 function 的喔
**function 參數解釋**
| Possible name | Supplied value |
| ------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `match` | The matched substring. (Corresponds to `$&` above.) |
| `p1, p2, ...` | The *n*th string found by a parenthesized capture group, provided the first argument to `replace()` was a [`RegExp`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp) object. (Corresponds to `$1`, `$2`, etc. above.) For example, if `/(\a+)(\b+)/`, was given, `p1` is the match for `\a+`, and `p2` for `\b+`. |
| `offset` | The offset of the matched substring within the whole string being examined. (For example, if the whole string was `'abcd'`, and the matched substring was `'bc'`, then this argument will be 1.) |
| `string` | The whole string being examined. |
```
function replacer(match, p1, p2, p3, offset, string) {
// p1 is nondigits, p2 digits, and p3 non-alphanumerics
return [p1, p2, p3].join(' - ');
}
var newString = 'abc12345#$*%'.replace(/([^\d]*)(\d*)([^\w]*)/, replacer);
console.log(newString); // abc - 12345 - #$*%
```