How can I check string to equality in JavaScript

Question

I'm nearly new to JavaScript.

I want to make a random-name generator where from a string array I get 5 random names. This works, but I want to add many names, and I want to check that no names are duplicated. Because of that, I wanted to make a textfield where I can write names, and with the button press a for-loop looks after the array index, and with an if-statement. T

his is the html code:

<div id="box">
    <p id="first"></p>
    <p id="second"></p>
    <p id="third"></p>
    <p id="fourth"></p>
    <p id="fifth"></p>
</div>
<br>
<input type="button" value="Generier Namen" id="button">

<div>
    <input type="text" placeholder="Name.." id="input">
    <input type="button" value="Checken" id="checkbutton">
    <p id="output"></p>
</div>

and this the JavaScript

let namesMale = ["Akemi", "Akechi", "Akihiko", "Akihiro", "Akira", "Amida", "Arata", "Daisuke", "Eichi", "Eiko", "Hajime", "Haru", "Haruo", "Hikaru", "Hiroshi", "Hiroyuki", "Hisoka", "Hoshi", "Isao", "Izanagi", "Kaori", "Kazuhiko", "Kenji", "Kentaro", "Kichi", "Kioshi", "Kitaro", "Kiyo", "Kiyoshi", "Koshiro", "Masahiro", "Masayuki", "Minori", "Mitsuo", "Namiyo", "Naoko", "Nikko", "Ozuru", "Raidon", "Renjiro", "Ryo", "Ryuji", "Sadao", "Satoshi", "Seiichi", "Shinichi", "Shuji", "Taiyo", "Takahiro", "Takeo", "Takiyo", "Taku", "Tama", "Tatsuo", "Tenchi", "Tetsuya", "Tomo", "Torio", "Toshi", "Toyo", "Tsutomu", "Yasashiku", "Yoshi", "Yoshikazu", "Yoshimitsu", "Yoshinori", "Yoshito", "Yoshiyuki", "Yuji", "Yuki", "Yukio", "Yutaka", "Yuudai", "Zinan"];

    document.getElementById("button").onclick = function() {
        let randomOne = Math.floor(Math.random() * namesMale.length);
        let randomTwo = Math.floor(Math.random() * namesMale.length);
        if(randomTwo == randomOne){
            let randomTwo = Math.floor(Math.random() * namesMale.length);
        }
        let randomThree = Math.floor(Math.random() * namesMale.length);
        if(randomThree == randomOne ||randomThree == randomTwo){
            let randomThree = Math.floor(Math.random() * namesMale.length);
        }
        let randomFour = Math.floor(Math.random() * namesMale.length);
        if(randomFour == randomOne || randomFour == randomTwo || randomFour == randomThree){
            let randomFour = Math.floor(Math.random() * namesMale.length);
        }
        let randomFive = Math.floor(Math.random() * namesMale.length);
        if(randomFive == randomOne || randomFive == randomTwo || randomFive == randomThree || randomFive == randomFour){
            let randomFive = Math.floor(Math.random() * namesMale.length);
        }

        document.getElementById("first").innerHTML = namesMale[randomOne];
        document.getElementById("second").innerHTML = namesMale[randomTwo];
        document.getElementById("third").innerHTML = namesMale[randomThree];
        document.getElementById("fourth").innerHTML = namesMale[randomFour];
        document.getElementById("fifth").innerHTML = namesMale[randomFive];
    }



    document.getElementById("checkbutton").onclick = function() {
        let input = document.getElementById("input").value;
        for(let i = 0; i <= namesMale.length; i++){
            console.log(namesMale[i]);
            if(input.equals(namesMale[i])){
                document.getElementById("output").innerHTML = "Existiert";
            }
            else{
                document.getElementById("output").innerHTML = "Existiert nicht";
            }
        }
    }


//  ####### Event Handler ####### 

    let pressTab = document.getElementById("button");
    pressTab.addEventListener("keyup", function(event){
        if(event.keyCode === 13){
            event.preventDefault();
            document.getElementById("set").click();
        }
    });

The way I want it to work works in C# and Java, but my problem is, that the chrome console says: Uncaught TypeError: input.equals is not a function

How can I make it works, because in the documentation I found nothing..

Edit: I forgot to say that "===" and "==" will get me (if the name is in the list or not) "Existiert nicht" in english "don't exist"

Shuffle the array, take the first n names from it. Much simpler and saner than what you’re doing. — deceze
– deceze ♦, Commented Mar 24, 2019 at 9:17
To add to @deceze's brilliant answer, here's how to shuffle the array: stackoverflow.com/questions/2450954/… — frhd
– frhd, Commented Mar 24, 2019 at 9:24
You are checking all names in the array, and for every name you set the output as “existiert” or “existiert nicht”. So unless it’s exactly the last name you’re checking, you’ll overwrite any “existiert” in the next loop iteration. But further, you’re looping one more than the array is long, so the last item will never match and you’ll always end up with “existiert nicht”. — deceze
– deceze ♦, Commented Mar 24, 2019 at 9:24
You should also be running into issues with your let inside if blocks; those variables aren’t accessible outside the if block. — deceze
– deceze ♦, Commented Mar 24, 2019 at 9:27

Syed Mehtab Hassan · Accepted Answer · 2019-03-24 09:35:11Z

You can use == to check the equality

let namesMale = ["Akemi", "Akechi", "Akihiko", "Akihiro", "Akira", "Amida", "Arata", "Daisuke", "Eichi", "Eiko", "Hajime", "Haru", "Haruo", "Hikaru", "Hiroshi", "Hiroyuki", "Hisoka", "Hoshi", "Isao", "Izanagi", "Kaori", "Kazuhiko", "Kenji", "Kentaro", "Kichi", "Kioshi", "Kitaro", "Kiyo", "Kiyoshi", "Koshiro", "Masahiro", "Masayuki", "Minori", "Mitsuo", "Namiyo", "Naoko", "Nikko", "Ozuru", "Raidon", "Renjiro", "Ryo", "Ryuji", "Sadao", "Satoshi", "Seiichi", "Shinichi", "Shuji", "Taiyo", "Takahiro", "Takeo", "Takiyo", "Taku", "Tama", "Tatsuo", "Tenchi", "Tetsuya", "Tomo", "Torio", "Toshi", "Toyo", "Tsutomu", "Yasashiku", "Yoshi", "Yoshikazu", "Yoshimitsu", "Yoshinori", "Yoshito", "Yoshiyuki", "Yuji", "Yuki", "Yukio", "Yutaka", "Yuudai", "Zinan"];
function findName(val) {
  for (let i = 0; i <= namesMale.length; i++) {
    console.log(namesMale[i]);
    if (val == namesMale[i]) {
      console.log("Existiert");
    } else {
      console.log("Existiert nicht");
    }
  }
}

findName('Yuki');

You can also use a function indexOf to find if particular string is present in an array

let namesMale = ["Akemi", "Akechi", "Akihiko", "Akihiro", "Akira", "Amida", "Arata", "Daisuke", "Eichi", "Eiko", "Hajime", "Haru", "Haruo", "Hikaru", "Hiroshi", "Hiroyuki", "Hisoka", "Hoshi", "Isao", "Izanagi", "Kaori", "Kazuhiko", "Kenji", "Kentaro", "Kichi", "Kioshi", "Kitaro", "Kiyo", "Kiyoshi", "Koshiro", "Masahiro", "Masayuki", "Minori", "Mitsuo", "Namiyo", "Naoko", "Nikko", "Ozuru", "Raidon", "Renjiro", "Ryo", "Ryuji", "Sadao", "Satoshi", "Seiichi", "Shinichi", "Shuji", "Taiyo", "Takahiro", "Takeo", "Takiyo", "Taku", "Tama", "Tatsuo", "Tenchi", "Tetsuya", "Tomo", "Torio", "Toshi", "Toyo", "Tsutomu", "Yasashiku", "Yoshi", "Yoshikazu", "Yoshimitsu", "Yoshinori", "Yoshito", "Yoshiyuki", "Yuji", "Yuki", "Yukio", "Yutaka", "Yuudai", "Zinan"];
function findName(val) {
  if (namesMale.indexOf(val) != -1) {
    console.log(val+" Existiert");
  } else {
    console.log(val+" Existiert nicht");
  }
}

findName('Yuki');
findName('ABC');

Bhojendra Rauniyar · Accepted Answer · 2019-03-24 09:16:15Z

0

String has no such method equals. Neither you have defined on its prototype. You could check rather like this:

if(input == namesMale[i]){

Or,

if(input === namesMale[i]){ // strictly compare

answered Mar 24, 2019 at 9:16

Bhojendra Rauniyar

86k36 gold badges179 silver badges241 bronze badges

1 Comment

Syed Mehtab Hassan Over a year ago

yeah == is equality operator while === also checks the type.

Prasad Telkikar · Accepted Answer · 2019-03-24 09:20:00Z

0

As per error mentioned in question you are facing error below

if(input.equals(namesMale[i])){  //Error is here, javascript does not contain .equal method
                document.getElementById("output").innerHTML = "Existiert";
            }
            else{
                document.getElementById("output").innerHTML = "Existiert nicht";
            }

You can try with

if(input === namesMale[i]) //=== triple equal to check type and value

or

 if(input == namesMale[i]) //== double equal for testing loose equality

edited Mar 24, 2019 at 9:20

answered Mar 24, 2019 at 9:16

Prasad Telkikar

16.1k7 gold badges26 silver badges49 bronze badges

3 Comments

Traijan Over a year ago

ahh, sorry I forgot to say, that with "===" I'll get with every name "don't exist"

Bhojendra Rauniyar Over a year ago

@Traijan Yeah, that doesn't exist in your array.

Traijan Over a year ago

@BhojendraRauniyar I mean, when I copy the name out of the array in the textfield to check, I get the output from the if statement "Existiert nicht" -> doesn't exist"

syntax-punk · Accepted Answer · 2019-03-24 09:20:54Z

0

Unfortunately, there is no equals function for strgins comparison in JavaScript. So, instean of that you can check if these two strings are equal with === operator. Overall, your function must look like:

document.getElementById("checkbutton").onclick = function() {
    let input = document.getElementById("input").value;
    for(let i = 0; i <= namesMale.length; i++){
        console.log(namesMale[i]);
        if(input === namesMale[i]){
            document.getElementById("output").innerHTML = "Existiert";
        }
        else{
            document.getElementById("output").innerHTML = "Existiert nicht";
        }
    }
}

Hope it helped, Cheers!

answered Mar 24, 2019 at 9:20

syntax-punk

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1 Comment

Traijan Over a year ago

sorry, I forgot to say that with "===" and "==" I get as output from the if statement "Existiert nicht" -> "don't exist" even though the name is in the array (copied) and I don't know why

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