javascript - How does 'function1(data, function2)' work? -

how these code work ?

function output(a) {   console.log( "the function filter return " + + "!"); }  x = function(data, fun) {   = data;   fun(a); };  theinput = " text input ";  x(theinput, output);//the function filter return  text input ! 

i wrote mysels , , works fine . don't understand how 'function1(data, function2)' run .

what x?

it variable holds reference function 2 parameters, data , fun.

whats doing here?

x(theinput, output); 

you call function passing string , function. yes, functions in javascript can treated other object. actually, objects. can stored variables (store reference them), can passed arguments function etc.

what happening inside body of function stored in x ?

initially, assign data variable called a , pass argument function output. function stored in output called.

if there 1 takeaway code snippet fact passed function argument function. important in javascript , associated nature of functions in javascript.

according mdn:

in javascript, functions first-class objects, i.e. objects , can manipulated , passed around other object. specifically, function objects.