Error in JavaScript code

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Error in JavaScript code

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#1 by (8 votes)
#2 by (2 votes)

4

I have a code snippet that looks in a Json field called campo , and inserts it into an array, which can not have repeated values. My array always returned undefined and it took me a while to find the error.
Why does JS and even IDE consider this valid? If campo is an array, then it is obvious that after . would call a method. There was no error in the browser.

Wrong code snippet:

while (i < listaContatos.length) {
   var dados = listaContatos[i].dados;
   for (var j = 0; j < dados.length; j++) {
       var nomeCampo = dados[j].campo;
       console.log(nomeCampo);
       if (campos.indexOf <= -1) {
           campos.push(nomeCampo);
         }
      }
   i++;
}

javascript sintaxe

asked by anonymous 29.07.2015 / 16:41

2 answers

2

campos.indexOf <= -1

When performing this comparison, you are comparing a function ("fields.indexOf") with an integer "-1". The comparison is valid since "indexOf" is an attribute of the Array object, although it is a function, but could be an integer as the "length" attribute.

29.07.2015 / 16:50

Script exchange image every reload Save a JSON in the bank vs. Relationship?

score 8 · Accepted Answer

It is not considered an error for some reasons.

The dot does not indicate that the method will be called, because for the call of a function the parentheses are mandatory. Otherwise you're just referencing the function as a variable. This makes the code valid because you are comparing a variable of type function with a variable of type number and JavaScript does not restrict it because of its poorly typed nature. In this case, the comparison will always return% with%

Second, if it is an array, dot notation can be used to refer to array indexes.

For example:

var meuArray = [];
meuArray['asd'] = 4;
console.log(meuArray.asd); // 4

It's perfectly possible to override the behavior of false and make that snippet of code work in an interesting way:

var meuArray = [];
meuArray['indexOf'] = -5;
console.log(meuArray.indexOf <= -1); // true
meuArray['indexOf'] = 5;
console.log(meuArray.indexOf <= -1); // false