Syntax Error in Basic Javascript Function

Question

I keep getting errors when debugging in IE. This is a basic hide function.

idHide is the id of the field to be hidden idCondition is the id of the reference field the condition is compared upon value is the value that would satisfy the condition

function hideOnCondition(idHide, idCondition, value)
{ 
 if (document.getElementById[idCondition] = value)
 { 
 document.getElementById(idHide).style.display = "none"; 
 }
 else
 { 
 document.getElementById(idHide).style.display = "";
 }
}

I always encounter the error in:

if (document.getElementById[idCondition] = value)

"the value of the property is null or undefined not a function object"

Then I tried changing "getElementById" with "all". then changed the brackets to parentheses, still nothing, only for the line to be highlighted in yellow.

Im sorry, I'm just stumped. Again, thank you all for understanding.

• Federico klez Culloca: = should be ==. Also I have to admit I've never seen document.getElementById treated like an associative array
• u_mulder: Do you know that comparison uses ==?
• gurvinder372: What is the syntax error? Please share a working snippet using <> in your toolbar.
• axiac: There is no syntax error, there is a runtime error and it is listed in the question. The question's title is incorrect.

Answer 1

• You were using square brackets instead of parentheses
• === should be used for comparing not =

.

function hideOnCondition(idHide, idCondition, value)
{ 
 if (document.getElementById(idCondition) === value) // <- fix here
 { 
 document.getElementById(idHide).style.display = "none"; 
 }
 else
 { 
 document.getElementById(idHide).style.display = "";
 }
}

• Reginald Maravilla: that I did not know, I was searching for other stuff about the code, but I didn't realize it was the equal sign. Thank you very much.
• Hendry: @ReginaldMaravilla you're welcome, if this matches what you need then please accept it as an answer

Answer 2

function myFunction(option, value, div) {
 //get the element you want to hide by it's ID
 var x = document.getElementById(div); 
 //if the option you selected is coresponding to the given value 
 //hide the earlier selected element
 if (option === value) {
 x.style.display = "none";
 } else {
 x.style.display = "block";
 }
}

This should do it.

• Andreas: While this code may answer the question, providing additional context regarding how and/or why it solves the problem would improve the answer's long-term value.
• Reginald Maravilla: Thank you, I think I get what your code does. Ill try to apply it to mine,

Answer 3

Instead of an assignment you should use the comparison operator Identity / strict equality (===):

function hideOnCondition(idHide, idCondition, value) {
 const result = document.getElementById[idCondition] === value ? 'none' : '';
 document.getElementById(idHide).style.display = result;
}

Answer 4

Two issues I could see

• using = instead of === and not comparing value instead only comparing the the output of document.getElementById[idCondition] with value.

• using [] instead of invoking the function using ()

Although, none of these would cause the syntax error as you have claimed in your post.

You can simplify it as

var getEl = (id) => document.getElementById(id);
function hideOnCondition(idHide, idCondition, value)
{ 
 getEl(idHide).style.display = getEl(idCondition).value == value ? "none" : "";
}