Variable not defined - javascript [duplicate]

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
– mic4ael, Commented Aug 19, 2016 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 Ruiz
– Alex Ruiz, Commented Aug 19, 2016 at 16:37
"do" is a JavaScript reserved word. I'd suggest to use other name. — Danny Fardy Jhonston Bermúdez
– Danny Fardy Jhonston Bermúdez, Commented Aug 19, 2016 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
– sagivasan, Commented Aug 19, 2016 at 16:46

randominstanceOfLivingThing · Accepted Answer · 2016-08-19 16:54:02Z

0

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)});

edited Aug 19, 2016 at 16:54

answered Aug 19, 2016 at 16:39

randominstanceOfLivingThing

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Comments

Akshay · Accepted Answer · 2016-08-19 16:38:03Z

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, 2016 at 16:38

Akshay

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Comments

philmtd · Accepted Answer · 2016-08-19 16:38:45Z

0

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);

answered Aug 19, 2016 at 16:38

philmtd

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Comments

Thalaivar · Accepted Answer · 2016-08-19 16:43:25Z

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, 2016 at 16:43

answered Aug 19, 2016 at 16:38

Thalaivar

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2 Comments

Heretic Monkey Over a year ago

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.

Thalaivar Over a year ago

@MikeMcCaughan: some typos... and invalids.. changed...

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