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Spy
Problem
Implement a spyOn function that does the following:
- Takes a function as its parameter
- Returns a spy function that takes any number of parameters
- spy calls func with the given arguments and returns what func returns
- spy has the following methods :
- .getCallCount( ) : returns the number of times spy has been called
- .wasCalledWith(val) : returns true if spy was ever called with val, else returns false
- .returned(val) : returns true if spy ever returned val, else returns false
Example
function add(a, b) { return a + b; }
var addSpy = spyOn( add );
addSpy.getCallCount(); // 0
addSpy(2, 4); // returns 6
addSpy.getCallCount(); // 1
addSpy(3, 5); // returns 8
addSpy.getCallCount(); // 2
addSpy.wasCalledWith(2); // true
addSpy.wasCalledWith(0); // false
addSpy.returned(6); // true
addSpy.returned(9); // falseSolution
var spyOn = function (func) {
var callCount = 0,
callVals = [],
retVals = [];
var spy = function () {
var args = [].slice.call(arguments);
var retVal = func.apply(this, args);
retVals.push(retVal);
callVals = callVals.concat(args);
callCount++;
return retVal;
};
spy.getCallCount = function () {
return callCount;
};
spy.wasCalledWith = function (val) {
return (callVals.indexOf(val) > -1);
};
spy.returned = function (val) {
return (retVals.indexOf(val) > -1);
};
return spy;
};The End
Spy
By Ivan Loughman-Pawelko
Spy
Technical interview problem on spies
