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I´m trying that when a value that is not in the array is introduced, it shows in the screen. So, when the find method doesn´t return undefined, it shows the value that has been introduced. But I don´t know why, it always return undefined.
Code:
<html>
<body>
<p id="demo"></p>
<input type="text" id="number">
<script>
var number = document.getElementById("number");
const array1 = [5, 12, 8, 98, 44];
var found = array1.find(element => element == number.value);
number.addEventListener("input", function(){
if(found == undefined){
document.getElementById("demo").innerHTML = number.value;
}
});
</script>
</body>
</html>
229
asked May 22 '26 11:05
You need to take the actual value from input in the event function as well as the find method. Otherwise you get the initial value from the input and the result of a find which does not match later inputs.
You could take Array#some instead of Array#find, because you have just numbers in the array. If you would have object and need one, find would work better here, because you get a different result than a simple number.
A word to Equality operator ==. This operator should be avoided, because it changes the type fo comparing with another value. Instead use Identity/strict equality operator ===, which checks the type and value.
const array1 = [5, 12, 8, 98, 44];
number.addEventListener("input", function() {
var number = document.getElementById("number"),
found = array1.some(element => element == number.value);
if (found) {
document.getElementById("demo").innerHTML = 'found';
} else {
document.getElementById("demo").innerHTML = 'not found: ' + number.value;
}
});<p id="demo"></p>
<input type="text" id="number">For a smarter approach take Array#includes` as check with a value as number as parameter.
const array1 = [5, 12, 8, 98, 44];
number.addEventListener("input", function() {
var number = document.getElementById("number").value;
if (array1.includes(+number)) {
document.getElementById("demo").innerHTML = 'found';
} else {
document.getElementById("demo").innerHTML = 'not found: ' + number;
}
});<p id="demo"></p>
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