Dynamically access function object property

Question

I need to check if the value of multiple textareas is equal to the property name of this object :

function make_test(name, job, ID) {
  test = {};
  test.name = name;
  test.job = job;
  test.ID = ID;
  return test;
}
  new make_test("Paul", "manager", 1);  //doesn't work
  new make_test("John", "employee", 2); //doesn't work
  new make_test("Jan", "employee", 2);  //works

It should only be a match if the value is equal to the name and if the index of the textarea is equal to the person's ID. For instance if I type "Paul" in textarea1, it should output paul's job : but it should not output it in textarea2 which should only output the job of persons having an ID = 2.

Problem : my code only works for the last person declared (Jan in this example). It's like the other persons don't even exist in the object, except for the last one. How can I fix this ?

I'm sure the answer is pretty obvious but I can't figure out what I'm doing wrong.

Demo here : https://jsfiddle.net/Lau1989/hxcpstty/

Thanks for your help

test is global ... so only the last test will be current ... you need to brush up on javascript — Jaromanda X
– Jaromanda X, Commented Oct 10, 2016 at 23:47
That's not a Costructor, it's a function that returns an Object. Object literals are already new. new is called to create an Object from a Constructor. — StackSlave
– StackSlave, Commented Oct 10, 2016 at 23:52
But it makes zero sense since you are making tests, but you store nothing that it is returning.... — epascarello
– epascarello, Commented Oct 10, 2016 at 23:52

jfriend00 · Accepted Answer · 2016-10-11 00:06:16Z

2

You need to declare test to be a local variable so all invocations of your function are not referring to the exact same global variable. When you don't declare your variable it becomes an implicit global variable which can lead to all sorts of problems. If you run your code in strict mode, the interpreter will flag this as an error for you too (which is generally helpful).

You also need to assign the return result from your function to a variable so you can reference the newly created object using that variable.

function make_test(name, job, ID) {
    var test = {};
 // ^^^
    test.name = name;
    test.job = job;
    test.ID = ID;
    return test;
}
var o1 = make_test("Paul", "manager", 1);
var o2 = make_test("John", "employee", 2);
var o3 = make_test("Jan", "employee", 2);

console.log(o1.name);   // "Paul"
console.log(o3.job);    // "employee"

You also don't need new in front of your function since you aren't using a system created object - you are just creating your own object and returning it. It will still work with new, but it is wasteful since you aren't using the object that the system will create with new.

If you want it to be an actual constructor function where you use new and could inherit the prototype, then do this:

function Make_test(name, job, ID) {
    this.name = name;
    this.job = job;
    this.ID = ID;
}

var o1 = new Make_test("Paul", "manager", 1);
var o2 = new Make_test("John", "employee", 2);
var o3 = new Make_test("Jan", "employee", 2);

Note, I used a capitalized constructor name here since it is a common convention to use initial cap names for constructor functions and initial lowercase names for regular functions.

You could also just remove the declaration entirely:

function make_test(name, job, ID) {
    return {name: name, job: job, ID: ID};
}

Or using ES6 syntax:

function make_test(name, job, ID) {
    return {name, job, ID};
}

edited Oct 11, 2016 at 0:06

answered Oct 10, 2016 at 23:49

jfriend00

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6 Comments

epascarello Over a year ago

but the way OP is using it, fixing the bug is not going to make the rest of the code run.

Lau Over a year ago

Thanks, I though it had to do with global variable at some point, but I still don't know how to access var test = {} properties within another function. Simply declaring it outside of make_test doesn't solve the problem

jfriend00 Over a year ago

@Lau - The code in your question doesn't really show what you're trying to do with the objects that make_test() creates. In my example, I assign them to another variable and you can use the newly created object by referring to the variable you assigned the new object to.

Lau Over a year ago

I'm trying to use them inside the boolean of function suggest(index) to access them all via their name (like I tried to do with test.name) instead of doing it with only one, using o1.name. Thanks for pointing it out though, I will edit my question to add this part of the code.

jfriend00 Over a year ago

@Lau - I've more than answered what you put in your original question and it doesn't work well on stack overflow if you just keep adding more problems to the same question. If you're still confused about other things, then maybe you should post a new question. It is not clear from your jsFiddle what you are trying to accomplish in your suggest() function. You could explain that in a new question.

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