JS common interview questions

map and forEach The difference between

1. map It's faster than forEach;
2. map Will return a new array , It doesn't change the original array ;forEach No new array will be returned , It is allowed to modify the original array ;
3. They all have parameters ：item、index、arr
4. Of internal anonymous functions this All points are window;

String to character array

1. split() Method

const text = "abc";
const chars = text.split('');
console.log(chars);
//['a', 'b', 'c']

2. Expand operator
   Expand operator ( …) Allow multiple elements when needed （ Such as array text ） Where to extend iteratable objects such as strings .
   This is an example of expanding a string into a character array . Correctly handle characters with two code units .

const text = "abc????";
const chars = [ ...text ];
console.log(chars);
//["a", "b", "c", "????"]

3. Deconstruct assignment
   Deconstruction assignment syntax can unpack the values in an array or an iteratable object into different variables .
   When deconstructing arrays or iteratable objects , We can use rest The pattern extracts the rest of it into a single variable .

const text = "abc????";
const [ ...chars ] = text;
console.log(chars);
//["a", "b", "c", "????"]

4. Array.from
   Array.from Assists in creating new arrays of objects that are arrayed or iterated . Strings are both iteratable and similar to arrays , therefore , It can be successfully converted to a character array .

const text = "abc????";
const chars = Array.from(text);
console.log(chars);
//["a", "b", "c", "????"]