What is the purpose of first parameter in Javascript concat() method?

Question

Consider the following code example demonstrating the usage of concat() method (Taken from W3Schools Javascript Tutorial):

<!DOCTYPE html>
<html>
  <body>

    <h2>JavaScript String Methods</h2>

    <p>The concat() method joins two or more strings:</p>

    <p id="demo"></p>

    <script>
    var text1 = "Hello";
    var text2 = "World!";
    var text3 = text1.concat(" ",text2);
    document.getElementById("demo").innerHTML = text3;
    </script>

  </body>
</html>

The output of above program is :

JavaScript String Methods

The concat() method joins two or more strings:

Hello World!

Now, if I want to concat the two words "Hello" and "World!" with a blank space added in between them I can make add a space at the end of the word "Hello " or at the beginning of the word " World!".

If above is the case then how should I do it using the concat() method? Do I still need to provide a blank space as first parameter in concat() method? Please explain me "What is the actual purpose of first parameter in concat method"? Also, explain me it is necessary?

Thanks.

You can add blank space to the "Hello" but that is hard-coded. What if "Hello" is coming from ajax call for example and you want to concatenate it with blank space? This is where the first parameter is useful. — Expressingx, May 23 '17 at 06:16
One more reason of not using `hello ` would be that you are changing the original string. It might be in your control sometime, but not always. Though you can use `+` to concat and it is ever recommended on [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/concat#Performance). — Rajesh, May 23 '17 at 06:21

score 1 · Accepted Answer · answered May 23 '17 at 06:17

1

String.concat(str1, str2, str3, ...., strN)

is accepting N number of parameter. This means it will glue all your parameters to one single string.

answered May 23 '17 at 06:17

Alexander_F

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score 0 · Answer 2 · answered May 23 '17 at 06:16

String.prototype.concat is a variadic function.

A variadic function takes a variable number of arguments.

In this case, the parameters are of type String, and are concatenated in the same order they appear.

NOTE: For JavaScript documentation, I strongly recommend Mozilla Developer Network to W3Schools.

score 0 · Answer 3 · answered May 23 '17 at 06:19

concat is not a global function, it is available either in array's instance or in string's instance.

In your case, you can use following code :-

String.prototype.concat("Hello ","World")

Here you are accessing concat function directly from the string's prototype

You can also use:-"Hello ".concat("World") // replace strings with variable if you want text1.concat(text2)

score 0 · Answer 4 · answered May 23 '17 at 06:19

This is useful when the second string (text2) is coming from a variable. For example out of a database, ajaxcalls, everything where you don't control it's content, so it's much cleaner and more readable doing it this way. Also maybe you could have a loop that generates a couple of codes with a "-" as seperator, it much easier to generate them this way.

It's just a way of working you could also use more parameters in the concat function.

score 0 · Answer 5 · answered May 23 '17 at 07:12

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/concat

please refer above link, it has expained multiple cases.

hope it will give answer.

here are multiple way you can concat sting in java-script https://sraji.wordpress.com/2011/01/10/multiple-ways-to-concatenate-a-string-in-javascript/

What is the purpose of first parameter in Javascript concat() method?

5 Answers5