I often hear words like parameter and/or argument used interchangeably with JS functions. Is a and b below both arguments or functions?
function example (a, b) {
// code here
}
If they are arguments then when does the term “parameter” come into play with JS functions?
a and b are, indeed, arguments. Values/objects that you provide to the function that the function uses for whatever purpose. Parameters is basically just another word for arguments.
HTH,
^ _ ^
Arguments can have multiple connotations, but there’s a technical difference too.
Parameters are the names of things listed by a function to be passed to it. a and b are parameters.
Arguments are the actual things passed to the function. If I said example(10,20), the 10 and 20 are the arguments of the function call.
There’s a secondary technical difference here.
What happens if i call example(10,20,30,40) ? Javascript isn’t strictly typed, so having too many arguments is still valid. But those extra bits, they get lost, because they’re not referencable right? Wrong.
All javascript functions have a hidden, public, constant Array in scope: arguments.
In my above call, arguments.length == 4 is true.
arguments[3] == 40.
Parameters are the names of things listed by a function to be passed to it. a and b are parameters.
Arguments are the actual things passed to the function. I
So, to be clear, parameters are like canons and arguments are like canon-balls??
More like… Parameters are the lines on the blueprint. Arguments are the bricks that make up the wall.
function buildWall(bricksoftypeA,bricksoftypeB) {
bricksofTypeA.forEach((brick) => placeBrick(brick));
bricksofTypeB.forEach((brick) => placeBrick(brick));
}
buildWall([brick1,brick3,brick5],[brick2,brick4,brick6,brick7]);
And the obvious follow-up… “When would I use that arguments thing?”
Most common answer: When you don’t know how many parameters to take.
function findBest() { //Note: No parameters declared, because I dont know.
var result = undefined;
arguments.forEach(function (x) {
// Needs some object validation here, which i ignore for brevity.
if (x.value > (result.value || -Infinity)) {
result = x;
}
});
return result; //Returns the best value, or undefined if nothing was sent in.
}
The arguments variable within a function is not an array but an object. The object has a length property but that is the only array-like property it has. Therefore doing
arguments.forEach(function(x){
// whatever
})
would not work. You can extract the arguments object into an array variable if you like.
var args = Array.prototype.slice.call(arguments);
var args = [].slice.call(arguments);
// ES2015
const args = Array.from(arguments);
[off-topic]
Can JavaScript accept parameters by reference as well as value?
[/off-topic]
No. Parameters are either passed by value (scalar values) or by reference (objects).
Sorry yes, you’re right, it’s a numerically indexed object. I would have actually used Object.keys(arguments).forEach((x) => ... arguments[x]...)
Well, technically no, a PARAMETER is neither, in the same way that it’s not a String, or an int. A Parameter is untyped, and so is indeterminate as to its disposition re: value vs reference. An ARGUMENT is either passed by reference or value.
function example(a,b) {
}
Before reading further, is a passed by reference or value? You don’t know.
example(100,0);
example("Quack",100);
In the first line, a is passed by value. In the second, it’s passed by reference.
I highly doubt that.
Well to be fair it depends on if the string is still the primitive or not. But if you want to be sure:
example({"c":"Wark"},100)
a is definitely NOT passed by value then, and the example holds true; the last call passes by reference, the first doesnt. What is the parameter? Neither, it’s just a placeholder name.
I was thinking about PHP (and C) how it is beneficial to pass large parameters by reference to eliminate the necessity for the function to make a local variable copy. Also the referenced parameter could be changed within the function and the function result would not be required.
Which is not a good coding practice IMO.
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