Javascript functions in an array

Question

I was tasked by my professor to make a simple Javascript program that displays simple math problems and their answers in a two dimensional table using a random number. Previously he gave us the example of using a function to write into a table like this:

function RandomGen() {
Random = math.floor(Math.random()*60);
    document.writeln("<th>");
       document.writeln(Random);
       document.writeln("</th>");
}
RandomGen();

In order to use an array, can I do this?

var RandomArray [

RandomGen(),
second_function(),
third_function(),
forth_function(),
]

RandomArray[0];

How do I append the functions together to write into a table?

Are you trying to store functions into an array and then run them from the array? — What have you tried
– What have you tried, Commented Mar 26, 2013 at 5:58
yes, and have the function write the html as well, at the professors request. — andrsnn
– andrsnn, Commented Mar 26, 2013 at 6:02

plalx · Accepted Answer · 2013-03-28 02:23:46Z

3

You almost got it. The correct syntax is:

var randomArray = [    
  RandomGen,
  second_function,
  third_function,
  forth_function
];

randomArray[0](); // this calls RandomGen
randomArray[1](); // this calls second_function

Remember the basic syntax rules:

A function name with no paranthesis is a function reference. It behaves just like any reference and so can be treated as a variable. Which means you can assign it to another variable, pass it into another function and as the example above stuff it into an array.
Adding paranthesis () to a function reference causes the function to be called. It doesn't matter if the function reference is a plain old function name or stored in another variable or stored in an array.

edited Mar 28, 2013 at 2:23

plalx

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answered Mar 26, 2013 at 6:19

slebetman

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Comments

Travis J · Accepted Answer · 2013-03-26 06:01:12Z

1

You can store the function in a variable, then put the variables in an array, and then access them from the array to call them.

var add = function(x,y){ return x + y; };
var multiply = function(x,y){ return x * y; };
var maths = [];
maths.push(add);
maths.push(multiply);
maths[0](1,2);//3
maths[1](3,4);//12

Conversely, you could do this with an object.

var maths = {};
maths.add = function(x,y){ return x + y; };
var four = maths.add(1,3);

Obviously you will have to modify these to match your exact situation.

answered Mar 26, 2013 at 6:01

Travis J

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5 Comments

andrsnn Over a year ago

gotcha, how would i then write into a table?

andrsnn Over a year ago

I keep pressing enter sorrylol document.writeln("<th>") maths[0](1,2); document.writeln("</th>")?

Travis J Over a year ago

@user2210274 - If you wanted maths content in the document.write it would be document.writeln("<th>"+maths[0](1,3)+"</th>"); where the + sigh concatenates the strings together. That would result in writing <th>4</th> to the page.

andrsnn Over a year ago

do you know how you would then print an element inthe array to the DOM into a html element using getelementbyid?

Travis J Over a year ago

@user2210274 - You would use the document.createElement and .appendChild methods. Here is a simple example: stackoverflow.com/a/15580994/1026459

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