If you have been in JavaScript for a while, you must know that the array sort function sort is a method in the array prototype, namely array.prototype.sort(), sort(compareFunction), where compareFunction is a comparison function. Let's take a look at a description from Mozilla MDN:
If compareFunction is not supplied, elements are sorted by converting them to strings and comparing strings in lexicographic ("dictionary" or "telephone book," not numerical) order. For example, "80" comes before "9" in lexicographic order, but in a numeric sort 9 comes before 80.
Here are some simple examples:
The code copy is as follows:
// Output [1, 2, 3]
console.log([3, 2, 1].sort());
// Output ["a", "b", "c"]
console.log(["c", "b", "a"].sort());
// Output [1, 2, "a", "b"]
console.log(["b", 2, "a", 1].sort());
As can be seen from the above example, the default is sorted in the alphabetical order of the dictionary.
Fortunately, sort accepts a custom comparison function, as shown in the following example:
The code copy is as follows:
function compareFunction(a, b) {
if( a > b) {
return -1;
}else if(a < b) {
return 1;
}else {
return 0;
}
}
//Outputs ["zuojj", "Benjamin", "1"]
console.log(["Benjamin", "1", "zuojj"].sort(compareFunction));
After sorting, we have another question: how to control ascending and descending order?
The code copy is as follows:
function compareFunction(flag) {
flag = flag ? flag : "asc";
return function(a, b) {
if( a > b) {
return flag === "desc" ? -1 : 1;
}else if(a < b) {
return flag === "desc" ? 1 : -1;
}else {
return 0;
}
};
}
//Outputs ["1", "Benjamin", "zuojj"]
console.log(["Benjamin", "1", "zuojj"].sort(compareFunction()));
//Outputs ["zuojj", "Benjamin", "1"]
console.log(["Benjamin", "1", "zuojj"].sort(compareFunction("desc")));
The sorting rules for comparisonFunction are as follows:
1.If it returns a negative number, a will be sorted to a lower index in the array.
2.If it returns a positive number, a will be sorted to a higher index.
3.And if it returns 0 no sorting is necessary.
Let's take a look at a passage excerpted from Mozilla MDN:
The behavior of the sort method changed between JavaScript 1.1 and JavaScript 1.2. To explain this description, let's look at an example:
In JavaScript 1.1, on some platforms, the sort method does not work. This method works on all platforms for JavaScript 1.2.
In JavaScript 1.2, this method no longer converts undefined elements to null; instead it sorts them to the high end of the array. Please click here for details.
The code copy is as follows:
var arr = [];
arr[0] = "Ant";
arr[5] = "Zebra";
//Outputs ["Ant", 5: "Zebra"]
console.log(arr);
//Outputs 6
console.log(arr.length);
//Outputs "Ant******Zebra"
console.log(arr.join("*"));
//Sort
var sortArr = arr.sort();
//Outputs ["Ant", "Zebra"]
console.log(sortArr);
//Outputs 6
console.log(sortArr.length);
//Outputs "Ant*Zebra****"
console.log(sortArr.join("*"));
I hope this article will be helpful for you to learn and understand the sort() method. I hope you will criticize and correct any inappropriate aspects in the article.
Reference link: https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/sort