Parameters & Default
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Expert Answer & Key Takeaways
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JavaScript Function Parameters
A JavaScript function does not perform any checking on parameter values (arguments).
1. Parameters vs Arguments
- Function Parameters are the names listed in the function definition.
- Function Arguments are the real values passed to (and received by) the function.
2. Default Parameters
If a function is called with missing arguments (less than declared), the missing values are set to
undefined.
ES6 allows function parameters to have default values:function myFunction(x, y = 10) {
return x + y;
}
myFunction(5); // Returns 153. The Arguments Object
JavaScript functions have a built-in object called the
arguments object. It contains an array of the arguments used when the function was called.function findMax() {
let max = -Infinity;
for (let i = 0; i < arguments.length; i++) {
if (arguments[i] > max) {
max = arguments[i];
}
}
return max;
}[!WARNING] Theargumentsobject is not a real Array. It looks like one but doesn't have methods likemaporforEach.
4. The Rest Parameter (...)
The rest parameter (
...) allows a function to treat an indefinite number of arguments as an array:function sum(...args) {
let sum = 0;
for (let arg of args) sum += arg;
return sum;
}
let x = sum(4, 9, 16, 25, 29, 100, 66, 77);Top Interview Questions
?Interview Question
Q:What happens if you pass more arguments than parameters?
A:
JavaScript doesn't throw an error. The extra arguments are ignored by the named parameters, but they are still accessible via the 'arguments' object or the rest parameter.
?Interview Question
Q:How do you set a default value for a parameter?
A:
You can assign a value directly in the function header: function myFunc(a = 1, b = 2) { ... }
?Interview Question
Q:What is the difference between the 'arguments' object and Rest parameters?
A:
The 'arguments' object is a local variable available within all functions (except arrow functions) and is array-like, but not a real array. Rest parameters (...args) are actual arrays and are the modern standard for handling indefinite arguments.
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