When brushing buttons, these functions are often used when dealing with string array problems, but it is always easy to confuse them. Now I will summarize them for the convenience of viewing next time.
One: Array.prototype.join()
The join() method concatenates all elements of an array (or an array-like object ) into a string and returns the string, separated by commas or the specified delimiter string. If the array has only one element, then that element will be returned without a separator.
const elements = ['Fire', 'Air', 'Water'];
console.log(elements.join());
// Expected output: "Fire,Air,Water"
console.log(elements.join(''));
// Expected output: "FireAirWater"
console.log(elements.join('-'));
// Expected output: "Fire-Air-Water"- If the parameters in the function are omitted , the array elements are separated by commas (
,) . If it is an empty string ("") , there will be no characters between any elements - If an element is undefined , it will be converted to an empty string
或 null
二：String.prototype.split()
The split() method splits a String object into an array of substrings using the specified delimiter string , using a specified split string to determine the position of each split.
const str = 'The quick brown fox jumps over the lazy dog.';
const words = str.split(' ');
console.log(words[3]);
// Expected output: "fox"
const chars = str.split('');
console.log(chars[8]);
// Expected output: "k"
const strCopy = str.split();
console.log(strCopy);
// Expected output: Array ["The quick brown fox jumps over the lazy dog."]- If the delimiter is omitted in str , the returned array contains one element consisting of the entire string
- If the delimiter is an empty string , return str as an array of each character in the original string
Note: If an empty string (") is used as the delimiter, the string is not between each user-perceived character (graphic pixel cluster), nor between each Unicode character (code point), but between between each UTF-16 code unit. This destroys surrogate pairs.
三：Array/String.prototype.slice()
The slice() method has both arrays and strings, and the usage methods are similar. The following uses arrays as an example to introduce
The slice() method returns a new array object, which is a shallow copy of the original array determined by begin and end (including begin, excluding end ). The original array will not be changed .
const animals = ['ant', 'bison', 'camel', 'duck', 'elephant'];
console.log(animals.slice(2));
// Expected output: Array ["camel", "duck", "elephant"]
console.log(animals.slice(-2));
// Expected output: Array ["duck", "elephant"]
console.log(animals.slice(2, 4));
// Expected output: Array ["camel", "duck"]
console.log(animals.slice(2, -1));
// Expected output: Array ["camel", "duck"]
console.log(animals.slice());
// Expected output: Array ["ant", "bison", "camel", "duck", "elephant"]