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1 sort function
The sort() method is used to sort the elements of the array and return the array.
默认排序顺序是在将元素转换为字符串, and then compare the sequence of points when their UTF-16 代码cell values were constructed.
2 try
const months = ['March', 'Jan', 'Feb', 'Dec'];
months.sort();
console.log(months); // ["Dec", "Feb", "Jan", "March"]
const arr = [1, 30, 4, 21, 100000];
arr.sort();
console.log(arr); // [1, 100000, 21, 30, 4]
3 Syntax & Parameters & Return Value
3.1 Grammar
Generally, it is more convenient to pass in one 比较函数, and the code is more readable.
// 无函数
sort()
// 箭头函数
sort((a, b) => {
/* … */ } )
// 比较函数
sort(compareFn)
// 内联比较函数
sort(function compareFn(a, b) {
/* … */ })
3.2 Parameters
compareFnUsed to specify 按某种顺序进行排列的函数. If omitted, the elements are sorted by the Unicode position of each character of the converted string.
a the first element to be compared
b the second element to compare
3.3 return value
The sorted array, ie 会改变的原数组.
4 Description and examples
If not specified compareFn, the element is converted to 字符串的诸个字符的 Unicode 点位进行排序.
For example, "Banana" would be sorted before "cherry".
When numbers are sorted from smallest to largest, 9 appears before 80, but because (unspecified compareFn), compared numbers are converted to strings first, "80" comes before "9" in Unicode order .
If specified compareFn, the array will be sorted by the return value of the function call. That is, a and b are the two elements to be compared:
- If
compareFn(a, b)greater than 0, b will be sorted before a. - If
compareFn(a, b)is less than 0, then a will be arranged before b; - If
compareFn(a, b)equal to 0, the relative positions of a and b remain unchanged. Note: The ECMAScript standard does not guarantee this behavior, and not all browsers will comply (e.g. Mozilla pre-2003); compareFn(a, b)Must always return the same comparison result for the same input, otherwise the result of the sort will be undefined.
compareFn(a, b)return value |
sort order |
|---|---|
> 0 |
a after b |
< 0 |
a before b |
=== 0 |
preserve the order of a and b |
4.1 The format of the comparison function is as follows
function compareFn(a, b) {
if (在某些排序规则中，a 小于 b) {
return -1;
}
if (在这一排序规则下，a 大于 b) {
return 1;
}
// a 一定等于 b
return 0;
}
To compare numbers instead of strings, the comparison function can simply be asubtracted b, and the following function will sort the array in ascending order (if it does not contain Infinityand NaN):
function compareNumbers(a, b) {
return a - b;
}
4.2 Function expressions are also convenient
const numbers = [4, 2, 5, 1, 3];
numbers.sort(function (a, b) {
return a - b;
});
console.log(numbers); // [1, 2, 3, 4, 5]
const numbers2 = [4, 2, 5, 1, 3];
numbers2.sort((a, b) => a - b);
console.log(numbers2); // [1, 2, 3, 4, 5]
5 Objects can be sorted according to a certain attribute order
Example:
const items = [
{
name: 'Edward', value: 21 },
{
name: 'Sharpe', value: 37 },
{
name: 'And', value: 45 },
{
name: 'The', value: -12 },
{
name: 'Magnetic', value: 13 },
{
name: 'Zeros', value: 37 }
];
//按 value 排序
items.sort((a, b) => a.value - b.value);
//按 name 排序
items.sort((a, b) => {
const nameA = a.name.toUpperCase(); // 不区分大小写
const nameB = b.name.toUpperCase(); // 不区分大小写
if (nameA < nameB) {
return -1;
}
if (nameA > nameB) {
return 1;
}
// name 必须相等
return 0;
});