[Javascript] Top Javascript Tips and Tricks

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In this post, We will discuss some of the tips and tricks that every javascript developer must know.

Boolean Expression

  • null, undefined, ' ' the empty string and 0 the number are all false boolean expression.
  • But be careful, '0' the string, [ ] the empty array, and {} the empty object are all true boolean expression.
so instead of using
if(x != null)
You can write the shorter format
if(x)
Similarly, if you want to check both null and empty. You can do like this:
if(x != null && x != ' ')
However, You can write short and nice
if(x)

Conditional Ternary Operator

Instead of this,
if (x) {
   foo();
} else {
   bar();
}

you can use the ternary operator,
return x ? foo( ) :bar( )

Short Circuit Operator

&& and ||, these operators are called as short circuit operators. Consider the following code.

function foo(x) {
   var win;
   if (x) {
      win = x;
   } else {
      win = window;
   }
}

You can rewrite above code as 

function foo(x) {
   var win = x || window;
}

&& is also used to reduce the lines of code, Please find the code below.

if (student) {
   if (student.name) {
      if (student.name[index]) {
         foo(student.name[index]);
      }
   }
}

You can rewrite the code as
if (student && student.name && student.name[index]) {
   foo(student.name[index]);
}

or, you can use a variable as,

var flag = student && student.name && student.name[index];
if (flag) {
   foo(student.name[index]);
}

Iteration using for loop:

For loop:

    var paragraphs = [1, 2, 3, 4, 5, 6];
    for (var i = 0; i < paragraphs.length; i++) {
       var paragraph = paragraphs[i];
       console.log(paragraph);
    }

Above code can be modified as below.

    var paragraphs = [1, 2, 3, 4, 5, 6];
    for (var i = 0, paragraph; paragraph = paragraphs[i]; i++) {
       console.log(paragraph);
    }

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Comments

  1. Anonymous2 August 2017 at 06:30

    The recommended for loop is dangerous IMHO.
    If the array contains a value that evaluates to false, the loop will be aborted prematurely, e.g. with var paragraphs = [1, 0, 4]; the console will only print 1.

    ReplyDelete
    Replies
    1. Raghu2 August 2017 at 09:47

      Above for loop is recommended option for "Iterating over Node Lists"

      var paragraphs = document.getElementsByTagName('p');
      for (var i = 0, paragraph; paragraph = paragraphs[i]; i++) {
      doSomething(paragraph);
      }


      In General, for...of statement is preferred check this post . http://www.nodesimplified.com/2017/07/javascript-list-of-dos-and-donts-in.html

      Delete

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