To replace a substring within a string in JavaScript - ECMAScript 2021, we use the replace() method that is available on a string. It takes two arguments:
1. The first argument is the substring or a regular expression pattern that we want to replace.
2. The second argument is the replacement string that should replace the existing substring.
Here are some examples:
1. Replacing a single occurrence of a substring:
let str = "The quick brown fox jumps over the lazy dog";
let newStr = str.replace("brown", "red");
console.log(newStr); // The quick red fox jumps over the lazy dog
In the above code, we replaced the first occurrence of "brown" with "red" in the original string.
2. Replacing all occurrences of a substring using regular expression:
let str = "The quick brown fox jumps over the lazy brown dog";
let newStr = str.replace(/brown/g, "red");
console.log(newStr); // The quick red fox jumps over the lazy red dog
In the above code, we used a regular expression with the g flag to replace all occurrences of "brown" with "red" in the original string.
3. Replacing a substring with a callback function:
let str = "The quick brown fox jumps over the lazy dog";
let newStr = str.replace(/brown|lazy/g, function(match) {
return match.toUpperCase();
});
console.log(newStr); // The quick BROWN fox jumps over the LAZY dog
In the above code, we used a regular expression with the g flag to match all occurrences of "brown" and "lazy". We passed a callback function to the replace() method that takes a match as an argument and returns the replacement string in uppercase.
These are just a few examples of how to replace a substring within a string in JavaScript - ECMAScript 2021. The replace() method is a powerful string manipulation tool and can be used in many different ways depending on the requirements of your project.