insert a string into another string at a specific index in javascript

One way to insert a string into another string at a specific index in JavaScript is to use the substr() method.

The substr() method extracts a part of a string and returns it as a new string. It takes two parameters: the starting index and the length of the substring to be extracted.

To insert a string, you can concatenate three substrings: the substring of the original string from 0 to the insertion index, the string to be inserted, and the substring of the original string from the insertion index to the end.

Here's an example:

index.tsx
let originalStr = "The quick brown fox jumps over the lazy dog.";
let index = 20;
let insertStr = "red ";

let newStr = originalStr.substr(0, index) + insertStr + originalStr.substr(index);

console.log(newStr); // "The quick brown fox red jumps over the lazy dog."
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In this example, we have an original string originalStr that contains a classic sentence. We want to insert the string "red " after the word "fox", which is located at index 20.

We declare a variable called index to keep track of the insertion index and a variable called insertStr to hold the string we want to insert.

We then create a new string newStr using the substr() method. The first substr() call extracts the substring of the original string from 0 to the insertion index ("The quick brown fox "), the second substr() call extracts the substring of the original string from the insertion index to the end ("jumps over the lazy dog."), and we concatenate those with the insertStr variable ("red ").

Finally, we log the new string to the console ("The quick brown fox red jumps over the lazy dog.").