Inserting string at position x of another string
JavascriptJavascript Problem Overview
I have two variables and need to insert string b
into string a
at the point represented by position
. The result I'm looking for is "I want an apple". How can I do this with JavaScript?
var a = 'I want apple';
var b = ' an';
var position = 6;
Javascript Solutions
Solution 1 - Javascript
var a = "I want apple";
var b = " an";
var position = 6;
var output = [a.slice(0, position), b, a.slice(position)].join('');
console.log(output);
Optional: As a prototype method of String
The following can be used to splice text
within another string at a desired index
, with an optional removeCount
parameter.
if (String.prototype.splice === undefined) {
/**
* Splices text within a string.
* @param {int} offset The position to insert the text at (before)
* @param {string} text The text to insert
* @param {int} [removeCount=0] An optional number of characters to overwrite
* @returns {string} A modified string containing the spliced text.
*/
String.prototype.splice = function(offset, text, removeCount=0) {
let calculatedOffset = offset < 0 ? this.length + offset : offset;
return this.substring(0, calculatedOffset) +
text + this.substring(calculatedOffset + removeCount);
};
}
let originalText = "I want apple";
// Positive offset
console.log(originalText.splice(6, " an"));
// Negative index
console.log(originalText.splice(-5, "an "));
// Chaining
console.log(originalText.splice(6, " an").splice(2, "need", 4).splice(0, "You", 1));
.as-console-wrapper { top: 0; max-height: 100% !important; }
Solution 2 - Javascript
var output = a.substring(0, position) + b + a.substring(position);
Edit: replaced .substr
with .substring
because .substr
is now a legacy function (per https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/substr)
Solution 3 - Javascript
You can add this function to string class
String.prototype.insert_at=function(index, string)
{
return this.substr(0, index) + string + this.substr(index);
}
so that you can use it on any string object:
var my_string = "abcd";
my_string.insertAt(1, "XX");
Solution 4 - Javascript
Using ES6 string literals, would be much shorter:
const insertAt = (str, sub, pos) => `${str.slice(0, pos)}${sub}${str.slice(pos)}`;
console.log(insertAt('I want apple', ' an', 6)) // logs 'I want an apple'
Solution 5 - Javascript
Maybe it's even better if you determine position using indexOf() like this:
function insertString(a, b, at)
{
var position = a.indexOf(at);
if (position !== -1)
{
return a.substr(0, position) + b + a.substr(position);
}
return "substring not found";
}
then call the function like this:
insertString("I want apple", "an ", "apple");
Note, that I put a space after the "an " in the function call, rather than in the return statement.
Solution 6 - Javascript
The Underscore.String library has a function that does Insert
> insert(string, index, substring) => string
like so
insert("Hello ", 6, "world");
// => "Hello world"
Solution 7 - Javascript
try
a.slice(0,position) + b + a.slice(position)
var a = "I want apple";
var b = " an";
var position = 6;
var r= a.slice(0,position) + b + a.slice(position);
console.log(r);
or regexp solution
"I want apple".replace(/^(.{6})/,"$1 an")
var a = "I want apple";
var b = " an";
var position = 6;
var r= a.replace(new RegExp(`^(.{${position}})`),"$1"+b);
console.log(r);
console.log("I want apple".replace(/^(.{6})/,"$1 an"));
Solution 8 - Javascript
If ES2018's lookbehind is available, one more regexp solution, that makes use of it to "replace" at a zero-width position after the Nth character (similar to @Kamil Kiełczewski's, but without storing the initial characters in a capturing group):
"I want apple".replace(/(?<=^.{6})/, " an")
var a = "I want apple";
var b = " an";
var position = 6;
var r= a.replace(new RegExp(`(?<=^.{${position}})`), b);
console.log(r);
console.log("I want apple".replace(/(?<=^.{6})/, " an"));
Solution 9 - Javascript
var array = a.split(' ');
array.splice(position, 0, b);
var output = array.join(' ');
This would be slower, but will take care of the addition of space before and after the an Also, you'll have to change the value of position ( to 2, it's more intuitive now)
Solution 10 - Javascript
Quick fix! If you don't want to manually add a space, you can do this:
var a = "I want apple";
var b = "an";
var position = 6;
var output = [a.slice(0, position + 1), b, a.slice(position)].join('');
console.log(output);
(edit: i see that this is actually answered above, sorry!)
Solution 11 - Javascript
Well just a small change 'cause the above solution outputs
> "I want anapple"
instead of
> "I want an apple"
To get the output as
> "I want an apple"
use the following modified code
var output = a.substr(0, position) + " " + b + a.substr(position);
Solution 12 - Javascript
With RegExp
replace
var a = 'I want apple';
var b = ' an';
var position = 6;
var output = a.replace(new RegExp(`^(.{${position}})(.*)`), `$1${b}$2`);
console.log(output);
Info: