Checking whether a string is empty in Javascript. Idiomatic or readable?

Question

I understand that it is often best to value the readability and clarity of the code by programming explicit. This does not only stop the Javascript, also the C#, Python and perhaps the rest of the programming languages.

I know these conventions are not rules, but they help in the development process if they are chosen at the right time, in the right environment and in the right way.

In Javascript to test whether a string is empty or not, you can use:

const value = '';
if(!value) {
    console.log('String vazia!');
}

This is because the empty string is a value defined as falsy (documentation). And in addition to comparing value with "", he compares with null and various other values.

Although it works, does this form not impair readability? It is not clear to a C# or Java developer that this if is the condition of an empty string.

In this case, explicitly comparing would harm an idiomatic Javascript code, why?

Answer 1

If the intention is really check whether the string is empty, then, yes, impairs the reading of the code and possibly the execution of it. The reason is that the comparison made in:

if (!value) {
    console.log("String vazia");
}

is not a check whether the string is empty, but yes if the value of value is falsy, as commented in the question itself. This implies that value, not to be a string empty, cannot be the integer zero, false, null, undefined, Nan (not a number), etc. However, all these values would be expected to pass the test "it is not a string "because they are not, in fact, a string empty (except the string empty proper). When I do if (!value), it is understood that value can be any value Truthy and not just one string unoccupied.

const testes = ["", false, null, undefined, NaN, [], 0, "Foo"];

for (let teste of testes) {
  if (!teste) {
    console.log("String vazia: " + teste);
  } else {
    console.log("Não é uma string vazia: " + teste);
  }
}

To actually check whether value is a string empty, you will have to check the type of the variable, whether using the typeof:

const testes = ["", false, null, undefined, NaN, [], 0, "Foo"];

for (let teste of testes) {
  if (typeof teste === "string" && teste.length == 0) {
    console.log("String vazia: " + teste);
  } else {
    console.log("Não é uma string vazia: " + teste);
  }
}

Note that when checking the type it becomes explicit that the desired is actually to search for strings empty, so all other values are valid.

That is to say using the rigid comparison with the operator ===, since == makes a loose comparison.

What’s a loose comparison?

const testes = ["", false, null, undefined, NaN, [], 0, "Foo"];

for (let teste of testes) {
  if (teste === "") {
    console.log("String vazia: " + teste);
  } else {
    console.log("Não é uma string vazia: " + teste);
  }
}

Again the check becomes explicit about its objective.

It is very important to point out that null is different from string empty. To maniero’s response about it shows graphically the difference.

Answer 2

You can use the class String to start a new variable of this type, see:

const myText = new String("Hello!");
console.log(myText.length); // Saída: 6 (tipo número)

const emptyText = new String("");
console.log(emptyText.length); // Saída: 0 (tipo número)

You can check the compatibility of this feature on MDN website