Home / Questions / 36197
Accepted
Máxima Alekz
Asked: 2020-11-27 17:52:29 +0800 CST 2020-11-27 17:52:29 +0800 CST

What is the difference between str.StringFunction(); a String(str).StringFunction();?

  • 772

In some codes I have seen the use of the replace function like the following.

var str = "Hola";
var converted = str.replace("a","o");
console.log(converted);

And I have also seen:

var str = "Hola";
var converted = String(str).replace("a","o");
console.log(converted);

Could you tell me what the difference is?

javascript

2 Answers

  1. Best Answer

    Really the only benefit that I see is that if you use String(str)it, it will not throw you any error if it Stringis null, instead, strit will throw an error.

    With your examples:

    var str = null;
var converted = str.replace("a","o");
console.log(converted); //Uncaught TypeError: Cannot read property 'replace' of null(…)(anonymous function)

var str = null;
var converted = String(str).replace("a","o");
console.log(converted); //null
    • 2

  2. Possible Differences:

    • If the value is NULLor undefinedwhen applying the replace() the first form will throw an Error Cannot read property 'replace' of undefinedEmphasizing that a replace() cannot be applied to said variable NULAor Indefinidawhile the second will Throw NULLor undefineddepending on how said variable was declared and initialized.

      var str ;
var converted = String(str).replace("1","2");
console.log(converted); /* Ouput undefined*/

var str ;
var converted = str.replace("1","2");
console.log(converted);/* Ouput Cannot read property 'replace' of undefined*/

    • Doing the CAST(conversion) of a Variable using String(str)allows us to ensure the replacein case the value of a variable is different to a string (int , double) obtaining the same results if the variable is NULLorundefined

      var str =2.2;
var converted = String(str).replace("2","4");
console.log(converted); /* Ouput 4.2*/
    • 2