CODEWITHSUNDEEP
html
fist-kim
fist-kim

Reputation: 31

how can boolean type is returned in this code?

<!DOCTYPE html>
<html>
<head>
<script>
    function clickCounter() {
    if(typeof(Storage) !== "undefined") {
        if (localStorage.clickcount) {//   <----- here!
            localStorage.clickcount = Number(localStorage.clickcount)+1;
        } else {
            localStorage.clickcount = 1;
        }
        document.getElementById("result").innerHTML = "You have clicked the button " + localStorage.clickcount + " time(s).";
    } else {
        document.getElementById("result").innerHTML = "Sorry, your browser does not support web storage...";
    }
}
</script>
</head>
<body>
<p><button onclick="clickCounter()" type="button">Click me!</button></p>
<div id="result"></div>
<p>Click the button to see the counter increase.</p>
<p>Close the browser tab (or window), and try again, and the counter will continue to count (is not reset).</p>
</body>
</html>

localStorage.clickcount <-- it returns boolean ???

I can't understand it. because there is no expression like == at all.

Upvotes: 1

Views: 43

Answers (3)

Lior
Lior

Reputation: 508

These cases return false:

boolean is false
number is 0\NaN
string is ''
var is undefined
var is null

otherwise -> return true

Upvotes: 0

Peter B
Peter B

Reputation: 24280

A term that you may see often in this context is truthy. MDN describes it as follows:

In JavaScript, a truthy value is a value that is considered true when evaluated in a Boolean context.

Source: Truthy

The if-statement wants/needs a boolean value. It checks what it got actually fed, and interprets that as either true (truthy) or false (falsy).

Upvotes: 1

Jean-Baptiste Yun&#232;s
Jean-Baptiste Yun&#232;s

Reputation: 36441

ECMASCript defines rules to convert expressions to boolean values:

9.2 ToBoolean

  • Number : The result is false if the argument is +0, -0, or NaN; otherwise the result is true.

Then the statement is equivalent to:

if (localStorage.clickcount != 0)

Upvotes: 4

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