I have an array of strings I need to sort in JavaScript, but in a case-insensitive way. How to perform this?
In (almost :) a one-liner
["Foo", "bar"].sort(function (a, b) {
return a.toLowerCase().localeCompare(b.toLowerCase());
});
Which results in
[ 'bar', 'Foo' ]
While
["Foo", "bar"].sort();
results in
[ 'Foo', 'bar' ]
myArray.sort(
function(a, b) {
if (a.toLowerCase() < b.toLowerCase()) return -1;
if (a.toLowerCase() > b.toLowerCase()) return 1;
return 0;
}
);
EDIT: Please note that I originally wrote this to illustrate the technique rather than having performance in mind. Please also refer to answer @Ivan Krechetov for a more compact solution.
It is time to revisit this old question.
You should not use solutions relying on toLowerCase. They are inefficient and simply don't work in some languages (Turkish for instance). Prefer this:
['Foo', 'bar'].sort((a, b) => a.localeCompare(b, undefined, {sensitivity: 'base'}))
Check the documentation for browser compatibility and all there is to know about the sensitivity option.
arr.sort(function(a,b) {
a = a.toLowerCase();
b = b.toLowerCase();
if (a == b) return 0;
if (a > b) return 1;
return -1;
});
If you want to guarantee the same order regardless of the order of elements in the input array, here is a stable sorting:
myArray.sort(function(a, b) {
/* Storing case insensitive comparison */
var comparison = a.toLowerCase().localeCompare(b.toLowerCase());
/* If strings are equal in case insensitive comparison */
if (comparison === 0) {
/* Return case sensitive comparison instead */
return a.localeCompare(b);
}
/* Otherwise return result */
return comparison;
});
You can also use the new Intl.Collator().compare, per MDN it's more efficient when sorting arrays. The downside is that it's not supported by older browsers. MDN states that it's not supported at all in Safari. Need to verify it, since it states that Intl.Collator is supported.
When comparing large numbers of strings, such as in sorting large arrays, it is better to create an Intl.Collator object and use the function provided by its compare property
["Foo", "bar"].sort(Intl.Collator().compare); //["bar", "Foo"]
Normalize the case in the .sort() with .toLowerCase().
The other answers assume that the array contains strings. My method is better, because it will work even if the array contains null, undefined, or other non-strings.
var notdefined;
var myarray = ['a', 'c', null, notdefined, 'nulk', 'BYE', 'nulm'];
myarray.sort(ignoreCase);
alert(JSON.stringify(myarray)); // show the result
function ignoreCase(a,b) {
return (''+a).toUpperCase() < (''+b).toUpperCase() ? -1 : 1;
}
The null will be sorted between 'nulk' and 'nulm'. But the undefined will be always sorted last.
You can also use the Elvis operator:
arr = ['Bob', 'charley', 'fudge', 'Fudge', 'biscuit'];
arr.sort(function(s1, s2){
var l=s1.toLowerCase(), m=s2.toLowerCase();
return l===m?0:l>m?1:-1;
});
console.log(arr);
Gives:
biscuit,Bob,charley,fudge,Fudge
The localeCompare method is probably fine though...
Note: The Elvis operator is a short form 'ternary operator' for if then else, usually with assignment.
If you look at the ?: sideways, it looks like Elvis...
i.e. instead of:
if (y) {
x = 1;
} else {
x = 2;
}
you can use:
x = y?1:2;
i.e. when y is true, then return 1 (for assignment to x), otherwise return 2 (for assignment to x).
This may help if you have struggled to understand:
var array = ["sort", "Me", "alphabetically", "But", "Ignore", "case"];
console.log('Unordered array ---', array, '------------');
array.sort(function(a,b) {
a = a.toLowerCase();
b = b.toLowerCase();
console.log("Compare '" + a + "' and '" + b + "'");
if( a == b) {
console.log('Comparison result, 0 --- leave as is ');
return 0;
}
if( a > b) {
console.log('Comparison result, 1 --- move '+b+' to before '+a+' ');
return 1;
}
console.log('Comparison result, -1 --- move '+a+' to before '+b+' ');
return -1;
});
console.log('Ordered array ---', array, '------------');
// return logic
/***
If compareFunction(a, b) is less than 0, sort a to a lower index than b, i.e. a comes first.
If compareFunction(a, b) returns 0, leave a and b unchanged with respect to each other, but sorted with respect to all different elements. Note: the ECMAscript standard does not guarantee this behaviour, and thus not all browsers (e.g. Mozilla versions dating back to at least 2003) respect this.
If compareFunction(a, b) is greater than 0, sort b to a lower index than a.
***/
arr.sort(function(a,b) {
a = a.toLowerCase();
b = b.toLowerCase();
if( a == b) return 0;
if( a > b) return 1;
return -1;
});
In above function, if we just compare when lower case two value a and b, we will not have the pretty result.
Example, if array is [A, a, B, b, c, C, D, d, e, E] and we use the above function, we have exactly that array. It's not changed anything.
To have the result is [A, a, B, b, C, c, D, d, E, e], we should compare again when two lower case value is equal:
function caseInsensitiveComparator(valueA, valueB) {
var valueALowerCase = valueA.toLowerCase();
var valueBLowerCase = valueB.toLowerCase();
if (valueALowerCase < valueBLowerCase) {
return -1;
} else if (valueALowerCase > valueBLowerCase) {
return 1;
} else { //valueALowerCase === valueBLowerCase
if (valueA < valueB) {
return -1;
} else if (valueA > valueB) {
return 1;
} else {
return 0;
}
}
}
I wrapped the top answer in a polyfill so I can call .sortIgnoreCase() on string arrays
// Array.sortIgnoreCase() polyfill
if (!Array.prototype.sortIgnoreCase) {
Array.prototype.sortIgnoreCase = function () {
return this.sort(function (a, b) {
return a.toLowerCase().localeCompare(b.toLowerCase());
});
};
}
Wrap your strings in / /i. This is an easy way to use regex to ignore casing
来源：https://stackoverflow.com/questions/8996963/how-to-perform-case-insensitive-sorting-in-javascript