How do I check whether a character in a string is a specific character in JavaScript?

Question

How do you check whether a character in a string is a specific character in JS? Currently I have code that checks each letter of a string and then goes through a huge if/else statement to check which letter it is, and I was wondering is there was a more efficient way to do this?

Example

var string = "hello"

I want it to test all five of the letters and see which letter it is and have it do something based on what letter it is, so if the first letter is h then run some code and if the first letter is a then do nothing and skip to the next letter to check.

Congrats on being a 13 yr old programmer!!! - that alone is impressive. Can you clarify the question please? what exactly do you want to find in the string? — blurfus, Jan 06 '17 at 22:28
Indeed, you may also want to clarify what you want to accomplish. — uncoder, Jan 06 '17 at 22:28
I'm not sure OP's intention is the same as the duplicate suggested — Jorg, Jan 06 '17 at 22:30
Could you please paste in your code, that way it may be easier to understand what you are trying to accomplish. — aggaton, Jan 06 '17 at 22:34
@Jorg This seemed the most reasonable interpretation. If the question is clarified and the meaning becomes different, ping me and I will reopen. — Oriol, Jan 06 '17 at 22:34
@Oriol I believe his updated version shows it is not the same question at all. — Alan Mimms, Jan 06 '17 at 23:06
You need to provide some code. Anyway, one way or another, you will have to stick to if/else (with ternaries code can be shorter), or switch/case, which is basically, more or less, the same... — sinisake, Jan 06 '17 at 23:34

score 1 · Answer 1 · answered Jan 06 '17 at 22:27

1

Example with JS

Check if a string includes with "world":

var str = "Hello world, welcome to the universe.";
var n = str.includes("world");

The result of n will be:

true

The same applies to single chars in a single word

Credits: http://www.w3schools.com/jsref/jsref_includes.asp

answered Jan 06 '17 at 22:27

SergioAMG

428
2
10

To me it doesn't seem your answer applies to the question being asked, although it's not all that clear what OP is asking. – Alan Mimms Jan 06 '17 at 22:42
User has edited the question, and based on new requirements, you are correct Alan, this is not answer he was looking for – SergioAMG Jan 06 '17 at 22:50
If I understand you correctly, you want to use something _other than_ a sequence of if ... else if ... statements to do this. You really will have to give us more to go on here. For example, post what your existing code looks like - however ugly it may be. If it shows what you're intending to accomplish someone will be more able to help guide you. As someone else said, congratulations on being a 13 year old programmer! Keep it up. It's worth it. – Alan Mimms Jan 06 '17 at 23:19
w3schools has a *lot* of misinformation, please prefer other resources (like MDN). – djechlin Jan 06 '17 at 23:41

score 1 · Accepted Answer · answered Jan 06 '17 at 23:37

There are many ways to accomplish this, you could for example have a series of if-else statements or a switch statement, I would suggest a different option though:

var str = 'hello',
        actions = { // Define actions (function to call) you want for specific characters
            h: function () {
                // Do something if character was 'h'
                console.log('h');
            },
            l: function () {
                // Do something if character was 'l'
                console.log('l');
            },
            o: function () {
                // Do something if character was 'o'
                console.log('o');
            }
        };

for (var i = 0; i < str.length; i++) {
    if (actions[str[i]]) { // If there is an action/function defined for the current character then call the function
        actions[str[i]]();
    }
}

This you you don't have to "know" what character you are currently on in the loop, only if something should happen for it.

And for reference, achieving the same thing with if-else statements:

var str = 'hello';
for (var i = 0; i < str.length; i++) {
    if (str[i] === 'h') {
        // Do something if character was 'h'
        console.log('h');
    }
    else if (str[i] === 'l') {
        // Do something if character was 'l'
        console.log('l');
    }
    else if (str[i] === 'o') {
        // Do something if character was 'o'
        console.log('o');
    }
}

And with switch statement:

var str = 'hello';
for (var i = 0; i < str.length; i++) {
    switch (str[i]) {
        case 'h':
            // Do something if character was 'h'
            console.log('h');
            break;
        case 'l':
            // Do something if character was 'l'
            console.log('l');
            break;
        case 'o':
            // Do something if character was 'o'
            console.log('o');
            break;
    }
}

Just made something similar (array of objects), but not sure about OP's context and efficiency: https://jsfiddle.net/trt9rpez/ :) — sinisake, Jan 06 '17 at 23:49

symcbean · Answer 3 · 2017-01-06T23:29:06.553

function do_something(str)
{
   switch (str.substr(0,1).tolower()) {
   case 'h':
     // call function something_else with the remainder of the string
     something_else(str.substr(1,str.length));
     break;
   case 'z':
     another_thing();
     break;
   default:
     // no need to explicitly add a case for 'h' - its handled here
     break;
   }
 }

switch is a multi-way branch. There are other ways to slice up the string. In practice there is unlikely to be a noticeable difference in performance between using a case statement compared with a sequence of if...else if....else if but it does make for better readability.

Some languages also provide constructs where you can define a routine to call at run time. This is also possible with javascript but makes it very easy to make bad mistakes and hard to debug/test/ them. The following is provided as an example of bad programming:

function fna()
{
    ...
}
function fnb()
{
    ...
}
...
function fnz()
{
  ...
}

var fn_to_call='fn' + str.substr(0,1).tolower() + '();';
eval(fn_to_call);

How do I check whether a character in a string is a specific character in JavaScript?

3 Answers3