--- id: a0b5010f579e69b815e7c5d6 title: 搜索與替換 challengeType: 5 forumTopicId: 16045 dashedName: search-and-replace --- # --description-- 在這道題目中,我們需要寫一個字符串的搜索與替換函數,它的返回值爲完成替換後的新字符串。 這個函數接收的第一個參數爲待替換的句子。 第二個參數爲句中需要被替換的單詞。 第三個參數爲替換後的單詞。 **注意:** 在更換原始單詞時保留原始單詞中第一個字符的大小寫。 即如果傳入的第二個參數爲 `Book`,第三個參數爲 `dog`,那麼替換後的結果應爲 `Dog` # --hints-- `myReplace("Let us go to the store", "store", "mall")` 應返回 `Let us go to the mall`。 ```js assert.deepEqual( myReplace('Let us go to the store', 'store', 'mall'), 'Let us go to the mall' ); ``` `myReplace("He is Sleeping on the couch", "Sleeping", "sitting")` 應返回 `He is Sitting on the couch`。 ```js assert.deepEqual( myReplace('He is Sleeping on the couch', 'Sleeping', 'sitting'), 'He is Sitting on the couch' ); ``` `myReplace("I think we should look up there", "up", "Down")` 應返回 `I think we should look down there`。 ```js assert.deepEqual( myReplace('I think we should look up there', 'up', 'Down'), 'I think we should look down there' ); ``` `myReplace("This has a spellngi error", "spellngi", "spelling")` 應返回 `This has a spelling error`。 ```js assert.deepEqual( myReplace('This has a spellngi error', 'spellngi', 'spelling'), 'This has a spelling error' ); ``` `myReplace("His name is Tom", "Tom", "john")` 應返回 `His name is John`。 ```js assert.deepEqual( myReplace('His name is Tom', 'Tom', 'john'), 'His name is John' ); ``` `myReplace("Let us get back to more Coding", "Coding", "algorithms")` 應返回 `Let us get back to more Algorithms`。 ```js assert.deepEqual( myReplace('Let us get back to more Coding', 'Coding', 'algorithms'), 'Let us get back to more Algorithms' ); ``` # --seed-- ## --seed-contents-- ```js function myReplace(str, before, after) { return str; } myReplace("A quick brown fox jumped over the lazy dog", "jumped", "leaped"); ``` # --solutions-- ```js function myReplace(str, before, after) { if (before.charAt(0) === before.charAt(0).toUpperCase()) { after = after.charAt(0).toUpperCase() + after.substring(1); } else { after = after.charAt(0).toLowerCase() + after.substring(1); } return str.replace(before, after); } ```