Syntax, Parameter and Return Value
Syntax: _
.ary(func, [n=func.length])
Parameters:
-
func (Function): The function to cap arguments for.
- [n=func.length] (number): The arity cap.
Return Value:
(Function) - Returns the new capped function.
Examples
Limiting Arguments for a Callback Function:
JavaScript
var _ = require('lodash');
function sum(a, b) {
return a + b;
}
var cappedSum = _.ary(sum, 2);
console.log(cappedSum(1, 2, 3));
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Output:
3
(ignores the third argument)
Demonstrates limiting a sum function to only two arguments.
Using with Array.map:
JavaScript
var numbers = [1, 2, 3];
var cappedParseInt = _.ary(parseInt, 1);
var parsedNumbers = numbers.map(cappedParseInt);
console.log(parsedNumbers);
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Output:
[1, 2, 3]
(avoids parseInt's second argument - radix)
Shows using _.ary() to avoid unexpected behavior with parseInt in Array.map.
Limiting Event Handler Arguments:
JavaScript
function logEvent(event, element) {
console.log('Event type:', event.type, 'on element:', element);
}
var cappedLogEvent = _.ary(logEvent, 1);
document.addEventListener('click', cappedLogEvent);
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Logs only the event object, ignoring the additional arguments provided by `addEventListener`.
An example of using _.ary() to limit arguments passed to an event handler.
Restricting Arguments in a Higher-Order Function:
JavaScript
function multiply(x, y, z) {
return x * y * z;
}
var double = _.ary(multiply, 2);
console.log(double(2, 3));
You can also try this code with Online Javascript Compiler
Output:
NaN (as third argument z is undefined)
Demonstrates capping a function to two arguments when used in a higher-order context.
Frequently Asked Questions
Can _.ary() handle default parameters in the capped function?
Yes, _.ary() can handle default parameters. However, it will only pass the first n arguments, and any default parameters beyond these will be used if needed.
What happens if n is larger than the number of parameters in func?
If n is larger than the function's parameters, _.ary() will still pass only the actual arguments provided to the function, up to n.
Is _.ary() commonly used in functional programming?
Yes, _.ary() is a common utility in functional programming to control function arity, especially when functions are used as arguments or callbacks in higher-order functions.
Conclusion
Lodash's _.ary() method is a useful tool for managing the arity of functions, particularly in scenarios involving callbacks, higher-order functions, or events. It ensures that functions only receive the number of arguments they are designed to handle, contributing to more predictable and stable code execution.
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