CODEWITHSUNDEEP
javascriptjquery
Dejo Dekic
Dejo Dekic

Reputation: 2126

When should you use parentheses inside an if statement's condition?

I have a if condition like so:

$(document).ready(function(){
  var name = 'Stack';
  var lastname = 'Overflow';
   if( name == 'Stack' && lastname == 'Overflow' )
   alert('Hi Stacker!');
});

So my alert is fired...

If I put my condition inside a brackets like this:

 $(document).ready(function(){
  var name = 'Stack';
  var lastname = 'Overflow';
   if( (name == 'Stack') && (lastname == 'Overflow') ){
      alert('Hi Stacker!');
   } 
});

My alert is also fired...

My question is: When and why I should use parentheses inside my if condition? Thank you!

Upvotes: 1

Views: 26051

Answers (9)

Chris Lemus
Chris Lemus

Reputation: 11

Conditional statements can be grouped together using parenthesis. And is not only limited to if statements. You can run the example below in your Chrome Developer Tools.

Example 1:

Console Execution

  false && false || true
  // true

flow

  false && false || true
    |        |        |
    |________|        |
    |                 |
    |                 |
  false     or      true
    |                 |
    |_________________|
               |
               |
              true

Example 2:

Console Execution

  false && (false || true)
  // false

flow

  false && (false || true)
    |              |        
    |______________|
    |
    |
  false

Helpful resources for playing around with JSInterpreter and AST's:

Upvotes: 0

Sunny
Sunny

Reputation: 4809

Brackets can be used, if multiple conditions needs to be checked.

For ex: User is also a Stacker if full name is 'StackOverflow' then add another condition with 'Or' operator. 

if(((name == 'Stack') && (lastname == 'Overflow')) || FullName =='StackOverflow')

As you can see, name and last name are placed inside one bracket meaning that it gives a result either true or false and then it does OR operation with FullName condition.

And having brackets around name, lastname and fullname fields are optional since it doesn't make any difference to the condition. But if you are checking other condition with FullName then group them into bracket.

Upvotes: 0

java seeker
java seeker

Reputation: 1266

first bracket requires for complex condition to ensure operator precedence correctly. lets say a example

   var x=1,y=1,z=0;
   
    if(x==0 && y==1 || z==0)   
    {
      //always true for any value of x
    }
    what will happen here  
    (0 && 1 ||1) ----> (0 ||1)----->1 
    && has high precedence over ||
   
    if(x==0 && (y==1 || z==0)) alert('1');
    {
     //correct way
    }

if you do not use (y==1 || z==0) bracket the condition always will be true for any value of x.

but if you use (..) the condition return correct result.

Upvotes: 0

mpm
mpm

Reputation: 20155

Because of operator precedence :

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Operator_Precedence

you'd better read this if you want more details

But basically == (equality) weights more than && (logical-and) , so A == B is evaluated before C && D given

C <- A == B

and 

D <- E == F

so adding parenthesis to C or D dont matter,in that specific situation.

Upvotes: 1

Arjit
Arjit

Reputation: 3456

Brackets () are used to group statements.

Ex - if you have an expression '2 + 3 * 5'.

There are two ways of reading this: (2+3)*5 or 2+(3*5).

To get the correct o/p based on operator precedence, you have to group the correct expression like * has higher precedence over +, so the correct one will be 2+(3*5).

Upvotes: 1

Smitt
Smitt

Reputation: 176

Consider the statement

if( i==10 || j == 11 && k == 12 || l == 13)

what you would want is if either i is 10 or j is 11 And either k is 12 or l is 13 then the result shouldbe true, but say if i is 10, j is 11, k is 10 and l is 13 the condition will fail, because the fate of equation is decided at k as aoon as && comes in picture. Now if you dont want this to happen the put it like this

if( (i==10 || j == 11) && (k == 12 || l == 13))

In this ORs will be executed first and the result will be true.

Upvotes: -1

MrPk
MrPk

Reputation: 2930

Brackets are never required in such situations. Of course, try to read first solution (without) and second solution (with). Second one it's clear, fast-readable and easy to mantain.

Of course if you have to change precedence (in this case you just have an AND condition, but what if you need and AND and an OR? 1 and 2 or 3 priority changes between "(1 and 2) or 3" - "1 and (2 or 3)"

Upvotes: 0

user908853
user908853

Reputation:

You use it to force associations, in your example this won't change anything. But consider this case:

A and B or C

is a lot different from

A and (B or C)

Here you would be preventing the expression from being understood as (A and B) or C which is the natural way javascript and maths do things.

Upvotes: 3

zogby
zogby

Reputation: 482

There is no much difference in your example. You can read that for reference Operator Precedence (JavaScript)

Upvotes: 5

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