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

To insert a substring into a string at a specific index in Typescript, you can use the combination of substr and splice functions.

Here's an example code snippet where we insert the substring "INSERTED_SUBSTRING" at index 4 of the string "ABCDEFGH":

index.ts
const originalString = "ABCDEFGH";
const indexToInsert = 4;
const substringToInsert = "INSERTED_SUBSTRING";

const modifiedString = originalString.substr(0, indexToInsert) +
                      substringToInsert +
                      originalString.substr(indexToInsert);
console.log(modifiedString); // ABCDINSERTED_SUBSTRINGEFGH
335 chars
9 lines

The substr function is used to split the original string into two substrings before and after the specified index. Then, we concatenate the first substring with the substring to be inserted, and then we concatenate the second substring.

Finally, the modifiedString variable holds the desired result which is "ABCDINSERTED_SUBSTRINGEFGH".