HIGHLIGHT
HIGHLIGHTED
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CFML allows trailing commas wherever a comma separated list of value can be provided and more values can be added. This feature is especially useful when working with long lists or when your code structure might change frequently
It allows:
- Easier Code Modifications
- Cleaner Version Control (Diffs)
- Reduced Syntax Errors
CFML allows trailing commas wherever a comma separated list of value can be provided and more values can be added. Trailing Commas are allowed at following places:
- [Array]
- [Struct]
- [Function Parameter]
- [Function calls]
- [Array and object destructuring]
Note:
- When using rest parameters, trailing commas are not allowed
- Rest elements cannot have a trailing comma
- Trailing comma is only allowed after non empty element
We will see how to use trailing commas under different scenarios.
1. Array with Trailing Comma
A trailing comma in an array is placed after the last element. It does not affect the array’s structure or content. It’s particularly useful when adding new elements to an array or when you want to keep your code tidy for future edits.
<cfscript>
arr = [ 1, 2, ]
writedump(arr) // 1,2
</cfscript>
Here, the trailing comma is added after
2. ColdFusion correctly identifies the array as [1, 2]
<cfscript>
array = [
"One",
"Two",
"Three",
];
writedump(arrayVar) // “One”,”Two”,”Three”
</cfscript>
In this example, the array has a trailing comma after the last element
"Three", but it does not affect the structure of the array. The output is the same as if the comma was omitted.<cfscript>
array = [
{name: "Vikas"},
{name: "Yadav"},
];
writedump(arrayVar)
</cfscript>
2. Struct with Trailing Comma
A struct can also have a trailing comma after the last key-value pair. Like arrays, it helps when adding or removing elements, especially in large objects.
<cfscript>
struct =
{
firstName: "Vikas",
lastName: "Yadav",
}
writedump(struct)
</cfscript>
3. Function Parameter Definitions with Trailing Comma
Trailing commas are supported in function parameter definitions, making it easier to manage parameters, especially in long parameter lists.
<cfscript>
function getFullName(firstName,lastName,) {
return firstName & " " & lastName
}
f = (a,b,) => a+b;
writedump(getFullName("Vikas","Yadav"))
writedump(f(2,3))
</cfscript>
4. Function calls with Trailing Comma:
<cfscript>
function getFullName(firstName,lastName) {
return firstName & " " & lastName
}
getFullName("Vikas","Yadav", )
max(10,20,)
</cfscript>
5. Array Destructuring with Trailing Comma:
Array destructuring allows you to unpack array elements into variables. ColdFusion 2025 allows trailing commas in destructuring assignments.
<cfscript>
// array destructuring with trailing comma
[a, b, ] = [10, 20];
writeDump(a);
writeDump(b);
</cfscript>
6. Object Destructuring:
<cfscript>
// object destructuring with trailing comma
o = {
p: 42,
q: true,
};
({ p, q, } = o);
writedump(p)
</cfscript>
A trailing comma is not allowed after the rest element (
...) in destructuring. The rest element is meant to gather all remaining elements, and adding a comma after it would create ambiguity.<cfscript>
arr = [100, 200, 300, 400, 500];
[firstVal, secondVal, ...rest, ] = arr; // not allowed
</cfscript>
Illegal trailing commas:
A trailing comma after the rest parameter or empty parameters is illegal, and will result in a syntax error.
function f(,) {}
(,) => {};
function f(...p,) {}
(...p,) => {}
[a, ...b,] = [1, 2, 3];
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Trailing Commas in ColdFusion
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