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JavaScript string method does not change the original string, but returns the new string; 1. toUpperCase() and toLowerCase() are used for case conversion; 2. trim() removes the beginning and end blanks, trimStart()/trimEnd() removes the beginning or end blanks respectively; 3. charAt(index) returns the character of the specified index, and returns an empty string when it is out of bounds; 4. indexOf() returns the index that appears for the first time in the substring, and returns -1 if it does not exist, include() returns a boolean value to indicate whether the substring is included; 5. replace() replaces the first match, and combines the regular g flag or replaceAll() to replace all matches; 6. slice(start, end) extracts the substring from start to end (not included), supporting negative indexes; 7. split(separator) is split into string arrays by delimiters; 8. substring() is similar to slice() but does not support negative indexing, substr(start, length) is intercepted by the starting position and length, but is deprecated; 9. startsWith() and endsWith() determine whether the string starts or ends with the specified content; 10. concat() connects multiple strings, but it is usually more convenient to use or template strings; select the appropriate method according to your needs to complete the search, extraction, formatting or segmentation operations.
JavaScript provides a variety of built-in string methods that allows you to manipulate and work with strings easily. Here are some of the most commonly used ones:
1. toUpperCase() and toLowerCase()
These methods return a new string with all characters converted to uppercase or lowercase.
"hello".toUpperCase(); // "HELLO" "HELLO".toLowerCase(); // "hello"
Useful for case-insensitive comparisons or formatting.
2. trim()
Removes whitespace from both ends of a string (spaces, tabs, newlines).
" hello ".trim(); // " hello"
There are also trimStart() and trimEnd() if you only want to trim one side.
3. charAt(index)
Returns the character at the specified index.
"hello".charAt(0); // "h"
You can also use brake notation: "hello"[0] — but charAt() is more explicit and returns an empty string if the index is out of bounds.
4. indexOf(substring) and includes(substring)
-
indexOf()returns the index of the first occurrence of a substring, or-1if not found. -
includes()returnstrueorfalsedepending on whether the substring exists.
"hello".indexOf("ll"); // 2
"hello".includes("ll"); // true includes() is often preferred for simple checks because it's more readable.
5. replace(searchValue, newValue)
Replaces the first occurrence of a substring (or pattern) with a new value.
"hello world".replace("world", "everyone"); // "hello everyone" To replace all occurrences, use a regular expression with the g flag:
"hello hello".replace(/hello/g, "hi"); // "hi hi"
Or in modern JS, use replaceAll() :
"hello hello".replaceAll("hello", "hi"); // "hi hi" 6. slice(start, end)
Extracts a portion of the string and returns a new string.
"hello".slice(1, 4); // "ell" "hello".slice(-3); // "llo" — negative index counts from the end
Be careful: slice() does not modify the original string.
7. split(separator)
Splits a string into an array of substrings based on a separator.
"hello world".split(" "); // ["hello", "world"]
"apple,banana,orange".split(","); // ["apple", "banana", "orange"]Useful for parsing text or extracting parts.
8. substring(start, end) and substr(start, length)
-
substring()is similar toslice()but doesn't accept negative indices. -
substr()takes a start index and a length (not end index). Note:substr()is deprecated.
"hello".substring(1, 4); // "ell" "hello".substr(1, 3); // "ell" — avoid this in new code
Prefer slice() over substr() .
9. startsWith() and endsWith()
Check if a string begins or ends with a certain substring.
"hello".startsWith("he"); // true
"hello".endsWith("lo"); // trueVery useful in routing, validation, or filtering.
10. concat()
Joins two or more strings.
"hello".concat(" ", "world"); // "hello world" But in practice, using or template literals is more common:
"hello" " " " " " world";
`hello ${"world"}`;Strings in JavaScript are immutable, so none of these methods change the original string — they all return a new one.
Basically, just pick the right tool for the job: search, extract, format, or split — there's likely a built-in method for it.
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