CODEWITHSUNDEEP
javascriptif-statement
Mr.Pandya
Mr.Pandya

Reputation: 2038

Unexpected token var when creating variable in if condition

I am creating variable and using it in for statement 

for(var i = 0; i < 10; i++) {
   console.log(i)
}

It is working properly and resulting from 1-10;

When I write same in the if condition

if(var value = 10) {
   console.log("Evaluate");
}

It is resulting Unexpected token var. When I declare a variable (var a = 10), resulting the same error. Is there any issue.

Upvotes: 0

Views: 482

Answers (4)

Mamun
Mamun

Reputation: 68923

When you write 

var value = 10

actually evaluated as the following statements:

var value;
value = 10

You can not write statement in if as condition, as the condition must be only expression:

An expression that is considered to be either truthy or falsy.

Upvotes: 1

node_man
node_man

Reputation: 1449

You need to declare the variable like this: 

    var value = 10;
    if(value == 10) {
       console.log("Evaluate");
    }

Upvotes: 0

Sam
Sam

Reputation: 325

Declare and initialize the variable outside. Use proper operators.

var value = 10;
if(value == 10) {
   console.log("Evaluate");
}
else {
    console.log("Hello");
}

Upvotes: 0

CertainPerformance
CertainPerformance

Reputation: 370999

An if statement only accepts an expression inside (something that evaluates to a value). Something like var value = ... is a statement - rather than evaluating to a value, it does something (namely, creates a local variable bound to the name value). So, since var value = ... cannot be evaluated as an expression, an error is thrown.

Some things can be evaluated both as statements and expressions (such as functions), but variable creation is not one of them.

Note that variable assignment is possible inside an if, because assignment does evaluate to the value assigned:

var value;
if(value = 10) {
  console.log('value now has the value 10');
}

But that's really confusing to read - a reader of the code will likely immediately worry whether that's a typo or not. Better to assign variables outside of an if condition, whenever possible.

Only use var when you want to create a new variable. If you simply want to check a variable (for example, check whether the variable named value is 10), then just print that variable name, and use a comparison operator (===, not =):

if (value === 10) {
  // do stuff
}

Upvotes: 2

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