@stdlib/utils
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Standard utilities.
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{{alias}}( fcn, arity, after[, thisArg] )
Decorates a provided function such that the function's return value is
provided as an argument to another function.
Decorators are intended to be transparent, meaning that, when interfacing
with an API, the decorated API should have the same signature (i.e., number
of parameters) as the decorated function.
Thus, a typical value for `arity` is `fcn.length`. This function does not
require equality, however, and the `arity` argument is allowed to diverge
from that of the decorated function. Specifying a differing `arity` does
*not* affect function evaluation behavior, as the returned function passes
all provided arguments to the decorated function.
If the `after` function returns `undefined`, the returned decorator returns
the return value of the decorated function `fcn`; otherwise, the returned
decorator returns the return value of `after`.
The returned decorator supports an `arity` less than or equal to `10` (i.e.,
the maximum arity of the returned function is `10`). For an arity greater
than `10`, the returned function has an arity equal to `0`. While this
violates strict notions of a decorator, for all practical purposes, this is
unlikely to be an issue, as the vast majority of functions have fewer than
`10` parameters and the need for explicitly checking function length is
relatively uncommon.
Common use cases for decorating a function with additional actions *after*
invocation include logging, capturing invocation statistics, and validating
return values.
Parameters
----------
fcn: Function
Function to decorate.
arity: integer
Number of parameters.
after: Function
Function with which to invoke the return value of the decorated
function.
thisArg: any (optional)
Evaluation context for `after`.
Returns
-------
out: Function
Decorator function.
Examples
--------
> function f( v ) { return -v; };
> var fcn = {{alias}}( {{alias:/math/base/special/abs}}, 1, f );
> var v = fcn( -5 )
-5
> v = fcn( 5 )
-5
{{alias}}.factory( fcn, arity, after[, thisArg] )
Uses code generation to decorate a provided function such that the
function's return value is provided as an argument to another function.
Code generation may be problematic in browser contexts enforcing a strict
content security policy] (CSP). If running in or targeting an environment
with a CSP, avoid using code generation.
For non-native functions, the function supports returning a decorator whose
API exactly matches the API of the decorated function, including function
length and parameter names.
For native functions, due to how native functions serialize to strings, the
function generates placeholder parameter names, which are unlikely to match
the canonical parameter names. Using placeholder parameter names ensures
that the length of the decorator (i.e., number of parameters) matches the
decorated function and, except in scenarios involving function source code
inspection, will not affect runtime behavior.
Parameters
----------
fcn: Function
Function to decorate.
arity: integer
Number of parameters.
after: Function
Function with which to invoke the return value of the decorated
function.
thisArg: any (optional)
Evaluation context for `after`.
Returns
-------
out: Function
Decorator function.
Examples
--------
> function f( v ) { return -v; };
> var fcn = {{alias}}.factory( {{alias:/math/base/special/abs}}, 1, f );
> var v = fcn( -5 )
-5
> v = fcn( 5 )
-5
See Also
--------