How does sort function work in JavaScript, along with compare function -

as asked: how sort function work in javascript, along compare function? if have array, , array.sort(compare) written in book if compare function returns a-b (two indices of array) works based on fact whether result greater 0, less 0 or equal 0. but, how work? not work out.

the "compare" function must take 2 arguments, referred a , b. make compare function return 0, greater 0, or less 0, based on these values, a , b.

1. return greater 0 if a greater b
2. return 0 if a equals b
3. return less 0 if a less b

with these 3 return values, , 2 arguments, possible write compare function can sort type of input data type, or complex data structures.

then, when call sort(), custom compare function, compare function called on pairs in to-be-sorted list, determine proper ordering.

lets walk through simple example... suppose you're sorting numbers, have simple compare function:

function compare(a,b) {     return - b; } 

simply subtracting b return greater 0 if larger b, 0 if equal, or less 0 if less b. meets requirements compare function.

now lets suppose our list of numbers sort:

var numbers = [1,5,3.14]; 

when call numbers.sort(compare), internally execute:

compare(1,5);     // returns -4, less b compare(1,3.14);  // return -2.14, less b compare(5,3.14);  // returns 1.86, greater b 

if you've ever done manual sorting or alphabetizing, you've done precisely same thing, without realizing it. though may have dozens or hundreds of items compare, you're comparing 2 numbers (or author's last names, or whatever) @ time. going through or short list of 3 numbers again, you'd start comparing first 2 numbers:

1. is 1 greater or less 5? less than, put these 2 numbers in our list: 1,5
2. is 3.14 greater or less 1? greater than, goes after 1 in new list
3. is 3.14 greater or less 5 in our new list? less than, goes before 5. our new list [1,3.14,5]

because can provide own compare() function, possible sort arbitrarily complex data, not numbers.