Sometimes, we may want to insert a JavaScript substring at a specific index of an existing string.
In this article, we’ll look at how to insert a JavaScript substring at a specific index of an existing string.
String.prototype.slice
We can call slice on a string with the start and end indexes to extract a substring from the start index to the end index minus 1.
So we can use it to break the existing string into 2 substrings with the index that we want to insert the substring to.
And we can put the substring in between the 2 broken substrings.
For instance, we can write:
const txt1 = 'foobaz'
const txt2 = txt1.slice(0, 3) + "bar" + txt1.slice(3);
console.log(txt2)
We have txt1 set to 'foobar' .
And we want to insert 'baz' between 'foo' and 'baz' .
To do this, we call slice with start index 0 and end index 3 to extract the segment between index 0 and 2.
And we call slice again to extract the substring from index 3 to the end of the string.
Then we concatenate the strings together with + .
So we get 'foobarbaz’ as a result.
String.prototype.substring
We can replace the slice method with the substring method.
It takes the same arguments as slice .
So we can write:
const txt1 = 'foobaz'
const txt2 = txt1.substring(0, 3) + "bar" + txt1.substring(3);
console.log(txt2)
And we get the same value for txt2 .
Conclusion
We can insert a substring into an existing at the existing index with the JavaScript string’s slice or substring methods.
