Spy decorator
importance: 5
Create a decorator spy(func) that should return a wrapper that saves all calls to function in its calls property.
Every call is saved as an array of arguments.
For instance:
function work(a, b) {
alert( a + b ); // work is an arbitrary function or method
}
work = spy(work);
work(1, 2); // 3
work(4, 5); // 9
for (let args of work.calls) {
alert( 'call:' + args.join() ); // "call:1,2", "call:4,5"
}P.S. That decorator is sometimes useful for unit-testing. Its advanced form is sinon.spy in Sinon.JS library.
The wrapper returned by spy(f) should store all arguments and then use f.apply to forward the call.
function spy(func) {
function wrapper(...args) {
// using ...args instead of arguments to store "real" array in wrapper.calls
wrapper.calls.push(args);
return func.apply(this, args);
}
wrapper.calls = [];
return wrapper;
}