Variable not defined - javascript

Question

I am coding an AI. It's not working. The browser is saying: Uncaught ReferenceError: do is not defined.

var what = ["jokes", "cats", "news", "weather", "sport"];

function start() {

    var do = what[Math.floor((Math.random() * what.length) + 1)];
}
start();
Document.write(do);

read about function scope in javascript (basically variables defined within function are only visible inside that function) — mic4ael, Aug 19 '16 at 16:36
Like mic4ael said, this is an issue with "scopes" in Javascript. 'do' is defined within a function, and thus not available outside. If you initialized 'do' outside of the function, you'll be able to access it. — Alex Johnson, Aug 19 '16 at 16:37
http://stackoverflow.com/documentation/javascript/480/scope#t=201608182147440316607 — Heretic Monkey, Aug 19 '16 at 16:37
"do" is a JavaScript reserved word. I'd suggest to use other name. — Danny Fardy Jhonston Bermúdez, Aug 19 '16 at 16:38
you should declare variable outsite function and `what[Math.floor(Math.random() * what.length) + 1]` here `+1` always return empty. try `what[Math.floor(Math.random() * what.length)]` — sagivasan, Aug 19 '16 at 16:46

score 0 · Answer 1 · answered Aug 19 '16 at 16:38

0

var what = ["jokes", "cats", "news", "weather", "sport"];
var do;
function start() {

    do = what[Math.floor((Math.random() * what.length) + 1)];
}
start();
Document.write(do);

answered Aug 19 '16 at 16:38

Akshay

815
7
16

Thalaivar · Answer 2 · 2016-08-19T16:43:25.827

0

do is a variable here and not a function.

var do = what[Math.floor((Math.random() * what.length) + 1)];

to create a do function, you would do something like this.

var what = ["jokes", "cats", "news", "weather", "sport"];
var do;
function start() {    
    do = function(){ return what[Math.floor((Math.random() * what.length) + 1)]};
}
start();
Document.write(do());

edited Aug 19 '16 at 16:43

answered Aug 19 '16 at 16:38

Thalaivar

23,282
5
60
71

And how would this work? Pretty sure that's invalid JavaScript you got there: `do = function() = {`? And `document.write(do)` would write `function() {...}`, not the result of calling the function. – Heretic Monkey Aug 19 '16 at 16:40
@MikeMcCaughan: some typos... and invalids.. changed... – Thalaivar Aug 19 '16 at 16:43

score 0 · Answer 3 · answered Aug 19 '16 at 16:38

Do is only present inside your function. Read about function scope :) Try this:

var what = ["jokes", "cats", "news", "weather", "sport"];
var do = undefined;
function start() {
    do = what[Math.floor((Math.random() * what.length) + 1)];
}
start();
Document.write(do);

randominstanceOfLivingThing · Accepted Answer · 2016-08-19T16:54:02.197

You do variable is out of scope

var what = ["jokes", "cats", "news", "weather", "sport"];

function start() {

    var do = what[Math.floor((Math.random() * what.length) + 1)];
}
start();
Document.write(do);

You need to change your code to

var what = ["jokes", "cats", "news", "weather", "sport"];

function start(callback) {

    var do = what[Math.floor((Math.random() * what.length) + 1)];
    callback(do);
}
start(function(val) {document.write(val)});

Variable not defined - javascript

4 Answers4