Html - Checking if a value is found in an array using user input

anonymous
August 6, 2023
305 views
3 votes
3 Answers

I am currently learning JavaScript Arrays and am trying to do a small program that allows a user to enter a value input. From there, once they click on the "Check" button, the JavaScript is meant to loop through the array and check if the value is found within.
If so, a success message is printed, if the value is not found the program prompts the user to try again.

My issue is I am having trouble with looping through the array to find the value. Below is all my code, and I would appreciate the help!

const numbers = [58, 4, 17, 32, 24, 53, 44, 99, 70, 56, 72,
  43, 36, 51, 37, 46, 35, 25, 29, 64, 76, 21,
  82, 94, 47, 12, 19, 31, 69, 81, 20, 91, 50,
  3, 34, 79, 2, 27, 68, 52, 23, 22, 84, 18, 16,
  33, 13, 39, 77, 8
];

let value = document.getElementById("num");
let output = document.getElementById("display");

function printValue() {
  for (let i = 0; i < numbers.length; i++) {
    if (value == i) {
      output.innerHTML = value.value;
      output.innerHTML = "Value was found in the array!"
    }
  }
  output.innerHTML = "Value is not found in array, please try again";

}

value.addEventListener("keyup", function(event) {
  if (event.keyCode === 13) {
    event.preventDefault();
    document.getElementById("sub").click();
  }
})

<h1>Check to see if your value is found in an array</h1>

<label for="num">Enter value:</label>
<input type="text" id="num" name="num">
<br><br>

<button id="sub" onclick="printValue()">Check</button>
<br><br>
<div id="display"></div>

Answers

There are few issues in your code:

You are comparing the element with the index where you should compare the element’s value with array value.
You have to return from the function after a match found.
I will also suggest you to convert the value to number and use strict equality (===) operator for checking. I will also suggest you to use textContent instead of innerHTML.

Try the following way:

<h1>Check to see if your value is found in an array</h1>

<label for="num">Enter value:</label>
<input type="text" id="num" name="num">
<br><br>

<button id="sub" onclick="printValue()">Check</button>
<br><br>
<div id="display"></div>

<script>
    const numbers = [58, 4, 17, 32, 24, 53, 44, 99, 70, 56, 72, 
                    43, 36, 51, 37, 46, 35, 25, 29, 64, 76, 21, 
                    82, 94, 47, 12, 19, 31, 69, 81, 20, 91, 50, 
                    3, 34, 79, 2, 27, 68, 52, 23, 22, 84, 18, 16, 
                    33, 13, 39, 77, 8];

    let inputEl = document.getElementById("num");
    let output = document.getElementById("display");
    function printValue() {
        let inputElVal = parseInt(inputEl.value); //get the value from the element
        for (let i = 0; i < numbers.length; i++) {
            if (inputElVal === numbers[i]) { //check the input element's value with array value.
                output.textContent = inputElVal;
                output.textContent = "Value was found in the array!";
                return; //return here
            }
        }
        output.innerHTML = "Value is not found in array, please try again";

    }

    inputEl.addEventListener("keyup", function(event){
        if (event.keyCode === 13) {
            event.preventDefault();
            document.getElementById("sub").click();
        }
    });

</script>

Though I prefer using Array.prototype.includes() instead for loop:

The includes() method determines whether an array includes a certain value among its entries, returning true or false as appropriate.

Code Example:

<h1>Check to see if your value is found in an array</h1>

<label for="num">Enter value:</label>
<input type="text" id="num" name="num">
<br><br>

<button id="sub" onclick="printValue()">Check</button>
<br><br>
<div id="display"></div>

<script>
    const numbers = [58, 4, 17, 32, 24, 53, 44, 99, 70, 56, 72, 
                    43, 36, 51, 37, 46, 35, 25, 29, 64, 76, 21, 
                    82, 94, 47, 12, 19, 31, 69, 81, 20, 91, 50, 
                    3, 34, 79, 2, 27, 68, 52, 23, 22, 84, 18, 16, 
                    33, 13, 39, 77, 8];

    let inputEl = document.getElementById("num");
    let output = document.getElementById("display");
    function printValue() {
        let inputElVal = parseInt(inputEl.value); //get the value from the element
        if (numbers.includes(inputElVal)) {
            output.textContent = "Value was found in the array!";
        } else {
            output.textContent = "Value is not found in array, please try again";
        }
        
    }

    inputEl.addEventListener("keyup", function(event){
        if (event.keyCode === 13) {
            event.preventDefault();
            document.getElementById("sub").click();
        }
    });

</script>

In your code you compare the input’s value to the for loop’s index which doesn’t have much sense. We should rather compare an array element.

There’s a nice method to check whether an array has a value: Array::includes().
But first we should convert the input’s value to a number and pass it to numbers.includes().
The problem here that parsing a string to a number is tricky. For example Number(' ') === 0 or parseInt('12asdf') === 12.

Here’s some parsing options of strings to numbers:
What is the standard way to check a variable is initialised as a number in javascript?

So for checking if a string contains only digits we could use a regular expression.
That could be considered advanced, so check the further easier solutions.

So our printValue() could be compressed to 2 lines:

Put the messages into an array:

const messages = ["Value is not found in array, please try again", "Value was found in the array!"];

Select an print message with:

output.innerHTML = messages[+(/^(-?[1-9]+d*|0)$/.test(inputEl.value) && numbers.includes(+inputEl.value))];

Here we

Test if the input contains only digits (with an optional sign and no leading zeros)
If successful test if the input’s values converted with to a number with + (which is the same as Number()) is in the numbers with Array::includes().
Convert the result boolean value to a number with + which will be the index of the corresponding message.

<h1>Check to see if your value is found in an array</h1>

<label for="num">Enter value:</label>
<input type="text" id="num" name="num" oninput="printValue()">
<br><br>

<div id="display"></div>

<script>
    const numbers = [-1, 0, 58, 4, 17, 32, 24, 53, 44, 99, 70, 56, 72, 
                    43, 36, 51, 37, 46, 35, 25, 29, 64, 76, 21, 
                    82, 94, 47, 12, 19, 31, 69, 81, 20, 91, 50, 
                    3, 34, 79, 2, 27, 68, 52, 23, 22, 84, 18, 16, 
                    33, 13, 39, 77, 8];

    let inputEl = document.getElementById("num");
    let output = document.getElementById("display");

    function printValue() {
        const messages = ["Value is not found in array, please try again", "Value was found in the array!"];
        output.innerHTML = messages[+(/^(-?[1-9]+d*|0)$/.test(inputEl.value) && numbers.includes(+inputEl.value))];
    }

</script>

But I guess for the OP’s purposes comparing strings is easier to understand.
We could use Array::some() to compare strings rather than numbers:

<h1>Check to see if your value is found in an array</h1>

<label for="num">Enter value:</label>
<input type="text" id="num" name="num" oninput="printValue()">
<br><br>

<div id="display"></div>

<script>
    const numbers = [-1, 0, 58, 4, 17, 32, 24, 53, 44, 99, 70, 56, 72, 
                    43, 36, 51, 37, 46, 35, 25, 29, 64, 76, 21, 
                    82, 94, 47, 12, 19, 31, 69, 81, 20, 91, 50, 
                    3, 34, 79, 2, 27, 68, 52, 23, 22, 84, 18, 16, 
                    33, 13, 39, 77, 8];

    let inputEl = document.getElementById("num");
    let output = document.getElementById("display");

    function printValue() {
        const messages = ["Value is not found in array, please try again", "Value was found in the array!"];
        output.innerHTML = messages[+numbers.some(num => num.toString() === inputEl.value)];
    }

</script>

Regarding the OP’s code it could be fixed as:

const numbers = [58, 4, 17, 32, 24, 53, 44, 99, 70, 56, 72,
  43, 36, 51, 37, 46, 35, 25, 29, 64, 76, 21,
  82, 94, 47, 12, 19, 31, 69, 81, 20, 91, 50,
  3, 34, 79, 2, 27, 68, 52, 23, 22, 84, 18, 16,
  33, 13, 39, 77, 8
];

let value = document.getElementById("num");
let output = document.getElementById("display");

function printValue() {
  for (let i = 0; i < numbers.length; i++) {
    if (value.value === numbers[i].toString()) {
      output.innerHTML = "Value was found in the array!"
      // here you should return to not allow to print the invalid messages
      return;
    }
  }
  output.innerHTML = "Value is not found in array, please try again";

}

value.addEventListener("keyup", function(event) {
  if (event.keyCode === 13) {
    event.preventDefault();
    document.getElementById("sub").click();
  }
})

<h1>Check to see if your value is found in an array</h1>

<label for="num">Enter value:</label>
<input type="text" id="num" name="num"><button id="sub" onclick="printValue()">Check</button>
<br><br>
<div id="display"></div>

Add return

function printValue() {
  for (let i = 0; i < numbers.length; i++) {
    if (value == i) {
      output.innerHTML = value.value;
      output.innerHTML = "Value was found in the array!"
      return
    }
  }
  output.innerHTML = "Value is not found in array, please try again";

}

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Html – Checking if a value is found in an array using user input

Answers