what does .split mean in javascript code example

Example 1: string split javascript

var myString = "An,array,in,a,string,separated,by,a,comma";
var myArray = myString.split(",");
/* 
*
*  myArray :
*  ['An', 'array', 'in', 'a', 'string', 'separated', 'by', 'a', 'comma']
*
*/

Example 2: split() javascript

let countWords = function(sentence){
    return sentence.split(' ').length;
}

console.log(countWords('Type any sentence here'));

//result will be '4'(for words in the sentence)