Is this code correct?

Question

1.00/5 (1 vote)

See more:

Hi All,
I'm struggling with JS, as you can see. Is it okay to use 2 parameters in a typeof? Also, will using 'if (!output) return false;' actually work to Verify that corresponding element is found? The program "works" (displays an answer), but I just want to be certain that the error checks are correct. I hope that made sense! I'm going to paste the whole code, just in case:

JavaScript

// today.js #2
// This script indicates the current date and time.

// This function is used to update the text of an HTML element.
// The function takes two arguments: the element's ID and the text message.
function setText(elementId, message) {
    'use strict';
    
    // Updated arguments so they cannot be an empty string - bullet #1
    // Updated arguments so they can also be a number - bullet #2
    if ( (typeof elementId == 'string' || Number)
            && (typeof message == 'string' || Number) )
    if ( (typeof elementId !== '')
            && (typeof message !== '') ){
  
        // Get a reference to the paragraph:
        var output = document.getElementById(elementId);
        
        //Verify that corresponding element is found - bullet #3
        if (!output) return false;
      
        // Update the innerText or textContent property of the paragraph:
		if (output.textContent !== undefined) {
			output.textContent = message;
		} else {
			output.innerText = message;
		}
    
    } // End of main IF.

} // End of setText() function.

// Call this function when the page has loaded:
function init() {
    'use strict';
    var today = new Date();
    var message = 'Right now it is ' + today.toLocaleDateString();
    message += ' at ' + today.getHours() + ':' + today.getMinutes();

    // Update the page:
    setText('output', message);
    
} // End of init() function.
window.onload = init;

Well, I'm in over my head here. This is from the textbook that I am using:

Quote:
Validate the function’s parameters:
if ( (typeof elementId == ‘string’)
&& (typeof message == ‘string’) ) {
This function can only work if it receives both values and both are of type
String (well, technically, the message could be a number).

Then the assignment was to:
Update today.js so that message can also be a number. And to update it so that it can't be an empty string.

I used this for the empty string:

JavaScript

if ( (typeof elementId !== '')
            && (typeof message !== '') )

but no amount of research gave me an indication of how to add so that the message could be a number. This is my first month, 3rd assignment in JS, so I thank you for any guidance that you can give me!

Posted 23-Feb-15 7:59am

Member 11139267

Updated 23-Feb-15 9:45am

v3

Add a Solution

Comments

Maciej Los 23-Feb-15 14:09pm

The question makes no sense...

Sergey Alexandrovich Kryukov 23-Feb-15 14:54pm

You are right. At the same time, some part of this question makes certain sense, so I provided detailed answer. There are few aspects to pay attention for.
Please see Solution 1.
—SA

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Sergey Alexandrovich Kryukov · Accepted Answer · 2015-02-23T08:53:00

Of course there cannot be "2 parameters in a typeof". One simple reason is this: typeof is, syntactically, operand, not a function, so, formally, it can have operand, no "parameters". Only one operand, no ifs no buts: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/typeof[^].

Moreover, having more then this only operand cannot make any sense.

The question makes no sense in the following sense: code can be right or wrong only if its purpose is known. Of course, it should be, in case of JavaScript, lexically correct. One wring comma or semicolon can make whole script invalid, not just the point with the error. (JavaScript is not the language which is executed one by one, as many mistakenly think; if the code has an error on lexical level, nothing executes, not even some correct part of it.)

Now, here is one problem with the type check you perform: for example, let's assume that some object is, say, string, but you could misspell the word 'string'. The check will always fail, even for strings, and nothing can tell you that the real reason is misspelled type name. So, I devised the following technique:

JavaScript

if (typeof message == typeof '') { /* ... */ }

[EDIT] I'll be very glad to see if someone suggests something better. [END EDIT]

At the same time, in nearly all cases, development should not rely on the type check. After all, JavaScript has too few types distinguished on this level. Even though I actually use the technique shown above, I only do it in some special cases, such as in my string formatting or object dump methods. It's better to rely on techniques where the type is exactly known.

For objects of the type 'object', you can check up that the two objects have the same origin checking up their constructors:

JavaScript

var obj1 = [1, 2, 3];
var obj2 = [4, 5];
var ofTheSameType12 = obj1.constructor === obj2.constructor; // true

function MyObject(id) { this.id = id; this.comment = 'some comment'; }
var obj3 = new MyObject(1);
var obj4 = new MyObject(200);
var ofTheSameType34 = obj3.constructor === obj3.constructor; // true
// true, despite the fact that obj3 and obj4 are logically different

function MyOtherObject(id) { this.id = id; this.comment = 'some comment'; }
var obj5 = new MyObject(1);
var obj6 = new MyOtherObject(1);
var ofTheSameType56 = obj5.constructor === obj6.constructor; // false
var ofTheSameType56NonStrict = obj5.constructor == obj6.constructor; // false
// false, despite the fact that obj5  and obj6 are logically identical

—SA