如何比较字符串字母（javascript）

Question

Hey I've been trying to write a simple javascript function for comparing string letters but i can't make it work for some reason...here is the code.

function compare(wordOne, wordTwo) {
    if (wordOne.substring(0) === wordTwo.substring(0))
    {
        return true;
    } else {
        return false;
    }
}
compare("house", "hell");

Answer 1

Assuming you want to compare the first letter of the two strings, you can use the following code

function compare(wordOne, wordTwo) {
    return wordOne[0] === wordTwo[0];
}
compare("house", "hell");

This condenses the if / else condition, as you are just interested in whether the first letters are equal - not in how different they are. You can also use str.toUpperCase() (or) str.toLowerCase() in order to make the comparison case insensitive.

As per @Josh Katofsky's suggestion, you can of course make this function more versatile by - for instance - adding a third parameter that tests the n-th letter:

function compare(wordOne, wordTwo, index) {
    return wordOne[index] === wordTwo[index];
}
compare("house", "hell", 0);

Answer 2

To explain why your current code doesn't work, you need to pass a second parameter to .substring as the to value. String.substring(0) just returns the whole string after the 0th character, so the entire word. Fixed example;

function compare(wordOne, wordTwo) {
    if (wordOne.substring(0, 1) === wordTwo.substring(0, 1)) {
        return true;
    }
    else 
    {
        return false;
    }
}

compare("house", "hell");

You could also just use wordOne[0] === wordTwo[0]

Answer 3

substring returns the part of the string between the start and end indexes, or to the end of the string .

If you want to compare only first character, use charAt

function compare(wordOne, wordTwo) {
   return wordOne.charAt(0) === wordTwo.charAt(0);
}
compare("house", "hell");

Or you can pass the index as the parameter

function compare(wordOne, wordTwo, index) {
   return wordOne.charAt(index) === wordTwo.charAt(index);
}
compare("house", "hell", 0);