Testing input length

Question

I want alert to pop if input letters length is equal to 0 but it is not working

<div class="rame">
    <input type=text placeholder="Name" style="position: relative; right:-750px" id="inp1">
    <input type=text placeholder="Name2" style="position: relative; right:-250px" id="inp2">
    <button onclick="check()">submit</button>
</div>

<script>
    function check() {
        var a = document.getElementById("inp1");
        var b = document.getElementById("inp2");
        if (a.length = 0) {
            alert("Hello World")
        }
    }
</script>

Obviously make sure popups are enabled in whatever browser used, and of course javascript itself. Try making an unconditional alert, and see if that works — JosephDoggie
– JosephDoggie, Commented Jun 4, 2019 at 14:50
Possible duplicate of How do I get the value of text input field using JavaScript? — Heretic Monkey
– Heretic Monkey, Commented Jun 4, 2019 at 14:52

Jan Turoň · Accepted Answer · 2019-06-04 14:51:20Z

4

You should call if(a.value.length==0). Note the difference between = and ==.

answered Jun 4, 2019 at 14:51

Jan Turoň

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3 Comments

Roman Meyer Over a year ago

or even better to use joda notation. if (0 == a.value.length) { ... } and then you'll never face this kind of misspell error headache

Jan Turoň Over a year ago

@RomanBobrik yoda notation :-) Let's use postfix aritmetic operators then :-)

Roman Meyer Over a year ago

no kidding, it is useful thing to avoid misspelling in conditions. saved a lot of time for me

Mario · Accepted Answer · 2019-06-04 14:59:15Z

2

With getElementById you will get an ELEMENT
In pure JavaScript length is meant for strings
If you want to compare you have to use double =

I think you tried this:

<div class="rame">
        <input type=text placeholder="Name" style="position: relative; right:-750px" id="inp1">
        <input type=text placeholder="Name2" style="position: relative; right:-250px" id="inp2">
        <button onclick="check()">submit</button>
    </div>

    <script>
        function check() {
            var a = document.getElementById("inp1");
            var b = document.getElementById("inp2");
            if (a.value.length == 0) {
                alert("Hello World")
            }
        }
    </script>

answered Jun 4, 2019 at 14:59

Mario

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