精心收集的有用的 JavaScript 代码片段，可以让你在 30 秒或更少的时间内理解。
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- 字符串换位组合(可重复)
- Average of array of numbers
- Capitalize first letter of every word
- Capitalize first letter
- Count occurrences of a value in array
- Current URL
- Curry
- Difference between arrays
- Distance between two points
- Escape regular expression
- Even or odd number
- Factorial
- Fibonacci array generator
- Filter out non-unique values in an array
- Flatten array
- et scroll position
- Greatest common divisor (GCD)
- Head of list
- Initial of list
- Initialize array with range
- Initialize array with values
- Last of list
- Measure time taken by function
- Object from key-value pairs
- Powerset
- Random number in range
- Randomize order of array
- Redirect to URL
- Reverse a string
- RGB to hexadecimal
- Scroll to top
- Similarity between arrays
- Sort characters in string (alphabetical)
- Sum of array of numbers
- Swap values of two variables
- Tail of list
- Unique values of array
- URL parameters
- UUID generator
- Validate number
比如字符串 "ab" 的所有换位组合字符串是 ["ab", "ba"]。而 "aab" 的所有换位组合是 ["aab", "aba", "aab", "aba", "baa", "baa"]（允许重复）。
使用递归。
对于给定字符串中的每个字母，为其余字母创建所有的换位组合。使用 map() 把当前字母和其余字母的换位组合结合起来，然后用 reduce() 把所有换位组合放到一个数组里。递归结束条件是字符串的 length 属性等于 2 或 1。
const anagrams = s => {
if(s.length <= 2) return s.length === 2 ? [s, s[1] + s[0]] : [s];
return s.split('').reduce( (a,l,i) => {
anagrams(s.slice(0,i) + s.slice(i+1)).map( v => a.push(l+v) );
return a;
}, []);
}Use reduce() to add each value to an accumulator, initialized with a value of 0, divide by the length of the array.
const average = arr =>
arr.reduce( (acc , val) => acc + val, 0) / arr.length;Use replace() to match the first character of each word and toUpperCase() to capitalize it.
const capitalizeEveryWord = str => str.replace(/\b[a-z]/g, char => char.toUpperCase());Use slice(0,1) and toUpperCase() to capitalize first letter, slice(1) to get the rest of the string.
Omit the lowerRest parameter to keep the rest of the string intact, or set it to true to convert to lower case.
const capitalize = (str, lowerRest = false) =>
str.slice(0, 1).toUpperCase() + (lowerRest? str.slice(1).toLowerCase() : str.slice(1));Use reduce() to increment a counter each time you encounter the specific value inside the array.
const countOccurrences = (arr, value) => arr.reduce((a, v) => v===value ? a + 1 : a + 0, 0);Use window.location.href to get current URL.
const currentUrl = _ => window.location.href;Use recursion.
If the number of provided arguments (args) is sufficient, call the passed function f.
Otherwise return a curried function f that expects the rest of the arguments.
const curry = f =>
(...args) =>
args.length >= f.length ? f(...args) : (...otherArgs) => curry(f)(...args, ...otherArgs)Use filter() to remove values that are part of values, determined using includes().
const difference = (arr, values) => arr.filter(v => !values.includes(v));Use Math.hypot() to calculate the Euclidean distance between two points.
const distance = (x0, y0, x1, y1) => Math.hypot(x1 - x0, y1 - y0);Use replace() to escape special characters.
const escapeRegExp = s =>
s.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
}Use Math.abs() to extend logic to negative numbers, check using the modulo (%) operator.
Return true if the number is even, false if the number is odd.
const isEven = num => Math.abs(num) % 2 === 0;Use recursion.
If n is less than or equal to 1, return 1.
Otherwise, return the product of n and the factorial of n - 1.
const factorial = n => n <= 1 ? 1 : n * factorial(n - 1)Create an empty array of the specific length, initializing the first two values (0 and 1).
Use reduce() to add values into the array, using the sum of the last two values, except for the first two.
const fibonacci = n =>
Array.apply(null, [0,1].concat(Array(n-2))).reduce(
(acc, val, i) => {
acc.push( i>1 ? acc[i-1]+acc[i-2] : val);
return acc;
},[]);Use Array.filter() for an array containing only the unique values.
const unique = arr => arr.filter(i => arr.indexOf(i) === arr.lastIndexOf(i));
// unique([1,2,2,3,4,4,5]) -> [1,3,5]Use recursion.
Use reduce() to get all elements that are not arrays, flatten each element that is an array.
const flatten = arr =>
arr.reduce( (a, v) => a.concat( Array.isArray(v) ? flatten(v) : v ), []);Use pageXOffset and pageYOffset if they are defined, otherwise scrollLeft and scrollTop.
You can omit el to use a default value of window.
const getScrollPos = (el = window) =>
( {x: (el.pageXOffset !== undefined) ? el.pageXOffset : el.scrollLeft,
y: (el.pageYOffset !== undefined) ? el.pageYOffset : el.scrollTop} );
// getScrollPos() -> {x: 0, y: 200}Use recursion.
Base case is when y equals 0. In this case, return x.
Otherwise, return the GCD of y and the remainder of the division x/y.
const gcd = (x , y) => !y ? x : gcd(y, x % y);Return arr[0].
const head = arr => arr[0];Return arr.slice(0,-1).
const initial = arr => arr.slice(0,-1);Use Array(end-start) to create an array of the desired length, map() to fill with the desired values in a range.
You can omit start to use a default value of 0.
const initializeArrayRange = (end, start = 0) =>
Array.apply(null, Array(end-start)).map( (v,i) => i + start );Use Array(n) to create an array of the desired length, fill(v) to fill it with the desired values.
You can omit v to use a default value of 0.
const initializeArray = (n, v = 0) =>
Array(n).fill(v);Return arr.slice(-1)[0].
const last = arr => arr.slice(-1)[0];Use performance.now() to get start and end time for the function, console.log() the time taken.
First argument is the function name, subsequent arguments are passed to the function.
const timeTaken = (f,...args) => {
var t0 = performance.now(), r = f(...args);
console.log(performance.now() - t0);
return r;
}Use map() to create objects for each key-value pair, combine with Object.assign().
const objectFromPairs = arr =>
Object.assign(...arr.map( v => {return {[v[0]] : v[1]};} ));Use reduce() combined with map() to iterate over elements and combine into an array containing all combinations.
const powerset = arr =>
arr.reduce( (a,v) => a.concat(a.map( r => [v].concat(r) )), [[]]);Use Math.random() to generate a random value, map it to the desired range using multiplication.
const randomInRange = (min, max) => Math.random() * (max - min) + min;Use sort() to reorder elements, utilizing Math.random() to randomize the sorting.
const randomizeOrder = arr => arr.sort( (a,b) => Math.random() >= 0.5 ? -1 : 1)Use window.location.href or window.location.replace() to redirect to url.
Pass a second argument to simulate a link click (true - default) or an HTTP redirect (false).
const redirect = (url, asLink = true) =>
asLink ? window.location.href = url : window.location.replace(url);Use array destructuring and Array.reverse() to reverse the order of the characters in the string.
Combine characters to get a string using join('').
const reverseString = str => [...str].reverse().join('');Convert each value to a hexadecimal string, using toString(16), then padStart(2,'0') to get a 2-digit hexadecimal value.
Combine values using join('').
const rgbToHex = (r, g, b) =>
[r,g,b].map( v => v.toString(16).padStart(2,'0')).join('');Get distance from top using document.documentElement.scrollTop or document.body.scrollTop.
Scroll by a fraction of the distance from top. Use window.requestAnimationFrame() to animate the scrolling.
const scrollToTop = _ => {
const c = document.documentElement.scrollTop || document.body.scrollTop;
if(c > 0) {
window.requestAnimationFrame(scrollToTop);
window.scrollTo(0, c - c/8);
}
}Use filter() to remove values that are not part of values, determined using includes().
const difference = (arr, values) => arr.filter(v => values.includes(v));Split the string using split(''), sort() utilizing localeCompare(), recombine using join('').
const sortCharactersInString = str =>
str.split('').sort( (a,b) => a.localeCompare(b) ).join('');Use reduce() to add each value to an accumulator, initialized with a value of 0.
const sum = arr =>
arr.reduce( (acc , val) => acc + val, 0);Use array destructuring to swap values between two variables.
[varA, varB] = [varB, varA];Return arr.slice(1).
const tail = arr => arr.slice(1);Use ES6 Set and the ...rest operator to discard all duplicated values.
const unique = arr => [...new Set(arr)];
// unique([1,2,2,3,4,4,5]) -> [1,2,3,4,5]Use match() with an appropriate regular expression to get all key-value pairs, map() them appropriately.
Combine all key-value pairs into a single object using Object.assign() and the spread operator (...).
Pass location.search as the argument to apply to the current url.
const getUrlParameters = url =>
Object.assign(...url.match(/([^?=&]+)(=([^&]*))?/g).map(m => {[f,v] = m.split('='); return {[f]:v}}));Use crypto API to generate a UUID, compliant with RFC4122 version 4.
const uuid = _ =>
( [1e7]+-1e3+-4e3+-8e3+-1e11 ).replace( /[018]/g, c =>
(c ^ crypto.getRandomValues(new Uint8Array(1))[0] & 15 >> c / 4).toString(16)
)Use !isNaN in combination with parseFloat() to check if the argument is a number.
Use isFinite() to check if the number is finite.
const validateNumber = n => !isNaN(parseFloat(n)) && isFinite(n);Icons made by Smashicons from www.flaticon.com is licensed by CC 3.0 BY.