Error javascript if

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4

I’m not able to make a condition with if for example:

asd=true;
if(asd=='true'){
   alert('funcionou');
}

but it seems that somehow it is not getting into the if

javascript html

4 answers

7


Asd is a value boleanus and cannot be treated as a string try the following:

var asd=true;
if(asd==true){
   alert('funcionou');
}

or

var asd=true;
if(asd){
   alert('funcionou');
}

5

Since you already answered, I’ll just give you a hint.

Some conventions (e.g. PHPCS, Pear package) do not even allow comparisons using double equal (==), but require triple (===). Why?

Comparing equality with == can be unpredictable:

asd == true // true
asd == 1 // true
asd == 'true' // false

But with === we have accurate results:

console.log(asd === true); // true
console.log(asd !== false); // true
console.log(asd === 1); // false
console.log(asd === false); // false

2

If you assign true a variable, so the expected minimum would be that compared to the same original value, the condition would pass... but you used something different in the comparison: 'true'.

In javascript, 'true' is not the same as true. The first is a string, that is, a text, in which the word is written true, the second is a boolean value, meaning true.

Completion: when comparing make sure that the type of objects being compared is compatible. If they are not, then possibly the comparison will fail.

1

You’re comparing two different types of variables.

Even though it is not a strict comparison, it will fail because they are not equal.

  • == normal comparison, ex: 1 == true // verdadeiro
  • === strict comparison, checks if the type is the same, ex: 1 == true // falso

The simplest way for you to compare something in javascript is true, assuming it is not false. Example:

var foo = true;
var bar = false;
if (foo) { /* vai executar pois foo existe e é alguma coisa */ }
if (bar) { /* não vai executar, pois bar é falso */}

You can test if something is not fake using !variavel, this will invert the value of the variable, first javascript will convert the variable to a testable value (boleano), then it will invert the value of the result and then apply the conditional.

Values converted to false:

  • false
  • 0
  • -0
  • ''
  • null
  • undefined
  • NaN

Different values from these will be converted to true.

When you want to ensure that a variable is exactly a false or true value you should make strict comparison:

var verdadeiro = true;
if (verdadeiro === true) { /* faça algo */ }

It is still possible to restrict that the variable is a specific value, for example:

var foo = verdadeiro === true;

That is, if the true variable is anything other than true, the foo will be false, even if it is an object or things that can be converted.

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