for loop - count a how many times a letter appears in javascript using indexOf - Stack Overflow

admin管理员组

文章数量:1343983

I am trying to count how many times a letter appears in a string using indexOf(). Could you advise me on where I am going wrong in my code. Thanks!

var string = 'Lets find l as many times as we can. Love is natural, love you lots';

var myFunc = function (letter) {
    newString = 0;
    for (var i = 0; i < letter.length; i += 1) {
        if (string.indexOf('l')) {
            newString += 1;
        }
    }
    return newString;
}

I am trying to count how many times a letter appears in a string using indexOf(). Could you advise me on where I am going wrong in my code. Thanks!

var string = 'Lets find l as many times as we can. Love is natural, love you lots';

var myFunc = function (letter) {
    newString = 0;
    for (var i = 0; i < letter.length; i += 1) {
        if (string.indexOf('l')) {
            newString += 1;
        }
    }
    return newString;
}

• javascript
• for-loop
• indexof

Share Improve this question Follow asked Jan 2, 2014 at 1:52 jstonejstone 44533 gold badges88 silver badges1919 bronze badges 8

• Are you insistent upon some method using .indexOf()? there are easier ways here. – Michael Berkowski Commented Jan 2, 2014 at 1:56
• @MichaelBerkowski - nope, I was just trying to understand how to use it. – jstone Commented Jan 2, 2014 at 2:00
• 1 string.search(/l/g) – adeneo Commented Jan 2, 2014 at 2:04
• string.split('').filter(function(e) {return e=='l'}).length – adeneo Commented Jan 2, 2014 at 2:13
• 2 Performance tests between P.S.W.G.'s, Adam Rackis', and my answers. – SomeShinyObject Commented Jan 2, 2014 at 2:36

 |  Show 3 more ments

3 Answers 3

Sorted by: Reset to default 8

Instead of this

if (string.indexOf('l')) {
    newString += 1;
}

You can use charAt or even direct indexing to check each letter of a string.

Like this

if (letter[i] == 'l') {
    newString += 1;
}

or this

if (letter.charAt(i) == 'l') {
    newString += 1;
}

Here's a FIDDLE

---

Note that if you were to use indexOf you'd want to call it directly on the string in question, like this

letter.indexOf('l')

The other answer is perfectly good, but in case you really want a solution using indexOf (as the title of your question suggests), you need to provide it a second parameter, to tell it where to start looking for the next occurrence:

var myFunc = function (str) {
    var i = 0, c = 0;
    do {
        i = str.indexOf('l', i);
    } while (++i && ++c);
    return c;
}

Demonstration

But, if using indexOf is not a requirement, you can simplify this to:

var myFunc = function (str) {
    return str.split('l').length - 1;
}

A recursive method if you are insistent upon indexOf:

var myFunc = function (str, letter) {
    var count = 0,
        p = str.indexOf(letter);

    if (p > -1) {
        count += (1 + myFunc(str.slice(p + 1, str.length - 1), letter));
    }

    return count;
};

Fiddle

本文标签： for loopcount a how many times a letter appears in javascript using indexOfStack Overflow