CODEWITHSUNDEEP
javascriptstring
Jiew Meng
Jiew Meng

Reputation: 88397

Insert a string at a specific index

How can I insert a string at a specific index of another string? 

 var txt1 = "foo baz"

Suppose I want to insert "bar " after the "foo" how can I achieve that?

I thought of substring(), but there must be a simpler more straight forward way.

Upvotes: 480

Views: 833357

Answers (21)

Vinod Poorma
Vinod Poorma

Reputation: 449

Hi I found it in this way to insert any string or char at any position

function strInsert(str, inxAt) {
  let newStr = (str.split("")).reduce((a, b, n) => {
    return n === inxAt ? a + "-" + b : a + b
  }, '')
  return newStr
}

console.log(strInsert("9998888", 3))

Upvotes: 0

Ben Aston
Ben Aston

Reputation: 55789

  1. Instantiate an array from the string
  2. Use Array#splice
  3. Stringify again using Array#join

The benefits of this approach are two-fold:

  1. Simple
  2. Unicode code point compliant

const pair = Array.from('USDGBP')
pair.splice(3, 0, '/')
console.log(pair.join(''))

Upvotes: 25

ChrisoLosoph
ChrisoLosoph

Reputation: 617

Still in 2023, it does not look like there is an insertion String method after looking at the inbuilt String methods in MDN's documentation.

There is a simple but wasteful one-liner that can do it and which wasn't mentioned yet.

Array.from(originalString, (c, i) => i == index ? insertString+c : c ).join("")

The advantage is obviously, that no additional variables are required. It can be used in expression-only-context.

(Note: negative indices are intensionally skipped, because they might have no valid meaning. -1 could have been produced by String.prototype.indexOf which actually means "no index".)

This one-liner inserts a string before the indexed character but you can easily modify it to insert after it or insert at a set of indices.

Array.from(originalString, (c, i) => indices?.includes?.(i) ? insertString+c : c ).join("")

This line is even slower of course. According to MDN, Sets can check faster for elements in average and therefore using them instead of arrays would speed things up.

Array.from(originalString, (c, i) => (indices?.has?.(i) ?? indices?.includes?.(i) ?? indices == i) ? insertString+c : c ).join("")

Finally, this one-liner replaces either a scalar (string or number), a set or an array of indices.

Upvotes: 0

Base33
Base33

Reputation: 3215

Here is a method I wrote that behaves like all other programming languages:

String.prototype.insert = function(index, string) {
  if (index > 0)
  {
    return this.substring(0, index) + string + this.substring(index, this.length);
  }

  return string + this;
};

//Example of use:
var something = "How you?";
something = something.insert(3, " are");
console.log(something)

Reference:

Upvotes: 162

esenkaya
esenkaya

Reputation: 428

Prototype should be the best approach as many mentioned. Make sure that prototype comes earlier than where it is used.

String.prototype.insert = function (x, str) {
    return (x > 0) ? this.substring(0, x) + str + this.substr(x) : str + this;
};

Upvotes: 0

Ryan Ore
Ryan Ore

Reputation: 1345

This is basically doing what @Base33 is doing except I'm also giving the option of using a negative index to count from the end. Kind of like the substr method allows.

// use a negative index to insert relative to the end of the string.

String.prototype.insert = function (index, string) {
  var ind = index < 0 ? this.length + index  :  index;
  return  this.substring(0, ind) + string + this.substr(ind);
};

Example: Let's say you have full size images using a naming convention but can't update the data to also provide thumbnail urls.

var url = '/images/myimage.jpg';
var thumb = url.insert(-4, '_thm');

//    result:  '/images/myimage_thm.jpg'

Upvotes: 21

Kamal Kant
Kamal Kant

Reputation: 1158

Well, we can use both the substring and slice method.

String.prototype.customSplice = function (index, absIndex, string) {
    return this.slice(0, index) + string+ this.slice(index + Math.abs(absIndex));
};


String.prototype.replaceString = function (index, string) {
    if (index > 0)
        return this.substring(0, index) + string + this.substr(index);

    return string + this;
};


console.log('Hello Developers'.customSplice(6,0,'Stack ')) // Hello Stack Developers
console.log('Hello Developers'.replaceString(6,'Stack ')) //// Hello Stack Developers

The only problem of a substring method is that it won't work with a negative index. It's always take string index from 0th position.

Upvotes: 6

Pierre
Pierre

Reputation: 163

I wanted to compare the method using substring and the method using slice from Base33 and user113716 respectively, to do that I wrote some code

also have a look at this performance comparison, substring, slice

The code I used creates huge strings and inserts the string "bar " multiple times into the huge string

if (!String.prototype.splice) {
    /**
     * {JSDoc}
     *
     * The splice() method changes the content of a string by removing a range of
     * characters and/or adding new characters.
     *
     * @this {String}
     * @param {number} start Index at which to start changing the string.
     * @param {number} delCount An integer indicating the number of old chars to remove.
     * @param {string} newSubStr The String that is spliced in.
     * @return {string} A new string with the spliced substring.
     */
    String.prototype.splice = function (start, delCount, newSubStr) {
        return this.slice(0, start) + newSubStr + this.slice(start + Math.abs(delCount));
    };
}

String.prototype.splice = function (idx, rem, str) {
    return this.slice(0, idx) + str + this.slice(idx + Math.abs(rem));
};


String.prototype.insert = function (index, string) {
    if (index > 0)
        return this.substring(0, index) + string + this.substring(index, this.length);

    return string + this;
};


function createString(size) {
    var s = ""
    for (var i = 0; i < size; i++) {
        s += "Some String "
    }
    return s
}


function testSubStringPerformance(str, times) {
    for (var i = 0; i < times; i++)
        str.insert(4, "bar ")
}

function testSpliceStringPerformance(str, times) {
    for (var i = 0; i < times; i++)
        str.splice(4, 0, "bar ")
}


function doTests(repeatMax, sSizeMax) {
    n = 1000
    sSize = 1000
    for (var i = 1; i <= repeatMax; i++) {
        var repeatTimes = n * (10 * i)
        for (var j = 1; j <= sSizeMax; j++) {
            var actualStringSize = sSize *  (10 * j)
            var s1 = createString(actualStringSize)
            var s2 = createString(actualStringSize)
            var start = performance.now()
            testSubStringPerformance(s1, repeatTimes)
            var end = performance.now()
            var subStrPerf = end - start

            start = performance.now()
            testSpliceStringPerformance(s2, repeatTimes)
            end = performance.now()
            var splicePerf = end - start

            console.log(
                "string size           =", "Some String ".length * actualStringSize, "\n",
                "repeat count          = ", repeatTimes, "\n",
                "splice performance    = ", splicePerf, "\n",
                "substring performance = ", subStrPerf, "\n",
                "difference = ", splicePerf - subStrPerf  // + = splice is faster, - = subStr is faster
                )

        }
    }
}

doTests(1, 100)

The general difference in performance is marginal at best and both methods work just fine (even on strings of length ~~ 12000000)

Upvotes: 1

Md Bilal Zafar
Md Bilal Zafar

Reputation: 1

Take the solution. I have written this code in an easy format:

const insertWord = (sentence,word,index) => {
    var sliceWord = word.slice(""),output = [],join; // Slicing the input word and declaring other variables
    var sliceSentence = sentence.slice(""); // Slicing the input sentence into each alphabets
    for (var i = 0; i < sliceSentence.length; i++) 
           {
        if (i === index) 
               { // checking if index of array === input index
            for (var j = 0; j < word.length; j++) 
                       {   // if yes we'll insert the word
                output.push(sliceWord[j]); // Condition is true we are inserting the word
                       }
            output.push(" "); // providing a single space at the end of the word
                 }
        output.push(sliceSentence[i]);  // pushing the remaining elements present in an array
            }
    join = output.join(""); // converting an array to string
    console.log(join)
    return join;
}

Upvotes: 0

Madmadi
Madmadi

Reputation: 2140

You can do it easily with regexp in one line of code

const str = 'Hello RegExp!';
const index = 6;
const insert = 'Lovely ';
    
//'Hello RegExp!'.replace(/^(.{6})(.)/, `$1Lovely $2`);
const res = str.replace(new RegExp(`^(.{${index}})(.)`), `$1${insert}$2`);
    
console.log(res);

"Hello Lovely RegExp!"

Upvotes: 8

Maheer Ali
Maheer Ali

Reputation: 36594

Using slice

You can use slice(0,index) + str + slice(index). Or you can create a method for it.

String.prototype.insertAt = function(index,str){
  return this.slice(0,index) + str + this.slice(index)
}
console.log("foo bar".insertAt(4,'baz ')) //foo baz bar

Splice method for Strings

You can split() the main string and add then use normal splice()

String.prototype.splice = function(index,del,...newStrs){
  let str = this.split('');
  str.splice(index,del,newStrs.join('') || '');
  return str.join('');
}


 var txt1 = "foo baz"

//inserting single string.
console.log(txt1.splice(4,0,"bar ")); //foo bar baz


//inserting multiple strings
console.log(txt1.splice(4,0,"bar ","bar2 ")); //foo bar bar2 baz


//removing letters
console.log(txt1.splice(1,2)) //f baz


//remving and inseting atm
console.log(txt1.splice(1,2," bar")) //f bar baz

Applying splice() at multiple indexes

The method takes an array of arrays each element of array representing a single splice().

String.prototype.splice = function(index,del,...newStrs){
  let str = this.split('');
  str.splice(index,del,newStrs.join('') || '');
  return str.join('');
}


String.prototype.mulSplice = function(arr){
  str = this
  let dif = 0;
  
  arr.forEach(x => {
    x[2] === x[2] || [];
    x[1] === x[1] || 0;
    str = str.splice(x[0] + dif,x[1],...x[2]);
    dif += x[2].join('').length - x[1];
  })
  return str;
}

let txt = "foo bar baz"

//Replacing the 'foo' and 'bar' with 'something1' ,'another'
console.log(txt.splice(0,3,'something'))
console.log(txt.mulSplice(
[
[0,3,["something1"]],
[4,3,["another"]]
]

))

Upvotes: 4

Sebastian Scholl
Sebastian Scholl

Reputation: 1105

I know this is an old thread, however, here is a really effective approach.

var tn = document.createTextNode("I am just  to help")
t.insertData(10, "trying");

What's great about this is that it coerces the node content. So if this node were already on the DOM, you wouldn't need to use any query selectors or update the innerText. The changes would reflect due to its binding.

Were you to need a string, simply access the node's text content property.

tn.textContent
#=> "I am just trying to help"

Upvotes: 6

VisioN
VisioN

Reputation: 145478

UPDATE 2016: Here is another just-for-fun (but more serious!) prototype function based on one-liner RegExp approach (with prepend support on undefined or negative index):

/**
 * Insert `what` to string at position `index`.
 */
String.prototype.insert = function(what, index) {
    return index > 0
        ? this.replace(new RegExp('.{' + index + '}'), '$&' + what)
        : what + this;
};

console.log( 'foo baz'.insert('bar ', 4) );  // "foo bar baz"
console.log( 'foo baz'.insert('bar ')    );  // "bar foo baz"

Previous (back to 2012) just-for-fun solution:

var index = 4,
    what  = 'bar ';

'foo baz'.replace(/./g, function(v, i) {
    return i === index - 1 ? v + what : v;
});  // "foo bar baz"

Upvotes: 19

user40521
user40521

Reputation: 2129

my_string          = "hello world";
my_insert          = " dear";
my_insert_location = 5;

my_string = my_string.split('');  
my_string.splice( my_insert_location , 0, my_insert );
my_string = my_string.join('');

https://jsfiddle.net/gaby_de_wilde/wz69nw9k/

Upvotes: 8

user113716
user113716

Reputation: 322622

You could prototype your own splice() into String.

Polyfill

if (!String.prototype.splice) {
    /**
     * {JSDoc}
     *
     * The splice() method changes the content of a string by removing a range of
     * characters and/or adding new characters.
     *
     * @this {String}
     * @param {number} start Index at which to start changing the string.
     * @param {number} delCount An integer indicating the number of old chars to remove.
     * @param {string} newSubStr The String that is spliced in.
     * @return {string} A new string with the spliced substring.
     */
    String.prototype.splice = function(start, delCount, newSubStr) {
        return this.slice(0, start) + newSubStr + this.slice(start + Math.abs(delCount));
    };
}

Example

String.prototype.splice = function(idx, rem, str) {
    return this.slice(0, idx) + str + this.slice(idx + Math.abs(rem));
};

var result = "foo baz".splice(4, 0, "bar ");

document.body.innerHTML = result; // "foo bar baz"

EDIT: Modified it to ensure that rem is an absolute value.

Upvotes: 299

Jake Stoeffler
Jake Stoeffler

Reputation: 2905

If anyone is looking for a way to insert text at multiple indices in a string, try this out:

String.prototype.insertTextAtIndices = function(text) {
    return this.replace(/./g, function(character, index) {
        return text[index] ? text[index] + character : character;
    });
};

For example, you can use this to insert <span> tags at certain offsets in a string:

var text = {
    6: "<span>",
    11: "</span>"
};

"Hello world!".insertTextAtIndices(text); // returns "Hello <span>world</span>!"

Upvotes: 18

user2133061
user2133061

Reputation:

Just make the following function:

function insert(str, index, value) {
    return str.substr(0, index) + value + str.substr(index);
}

and then use it like that:

alert(insert("foo baz", 4, "bar "));

Output: foo bar baz

It behaves exactly, like the C# (Sharp) String.Insert(int startIndex, string value).

NOTE: This insert function inserts the string value (third parameter) before the specified integer index (second parameter) in the string str (first parameter), and then returns the new string without changing str!

Upvotes: 93

Inoperable
Inoperable

Reputation: 1509

You can use Regular Expressions with a dynamic pattern.

var text = "something";
var output = "                    ";
var pattern = new RegExp("^\\s{"+text.length+"}");
var output.replace(pattern,text);

outputs: 

"something      "

This replaces text.length of whitespace characters at the beginning of the string output. The RegExp means ^\ - beginning of a line \s any white space character, repeated {n} times, in this case text.length. Use \\ to \ escape backslashes when building this kind of patterns out of strings.

Upvotes: 4

mudshark2005
mudshark2005

Reputation: 47

another solution, cut the string in 2 and put a string in between.

var str = jQuery('#selector').text();

var strlength = str.length;

strf = str.substr(0 , strlength - 5);
strb = str.substr(strlength - 5 , 5);

jQuery('#selector').html(strf + 'inserted' + strb);

Upvotes: 3

Tim Down
Tim Down

Reputation: 324737

Inserting at a specific index (rather than, say, at the first space character) has to use string slicing/substring:

var txt2 = txt1.slice(0, 3) + "bar" + txt1.slice(3);

Upvotes: 606

David Hedlund
David Hedlund

Reputation: 129832

Given your current example you could achieve the result by either

var txt2 = txt1.split(' ').join(' bar ')

or

var txt2 = txt1.replace(' ', ' bar ');

but given that you can make such assumptions, you might as well skip directly to Gullen's example.

In a situation where you really can't make any assumptions other than character index-based, then I really would go for a substring solution.

Upvotes: 10

Related Questions