describe("About Functions And Closure (topics/12_about_functions_and_closure.js)", function () {

it("defining functions directly", function () {

let result = "a";

function changeResult() {

// the ability to access a letiables defined in the same scope as the function is known as 'closure'

result = "b";

}

changeResult();

expect(__).toBe(result, "what is the value of result?");

});

it("assigning functions to letiables", function () {

const triple = function (input) {

return input * 3;

};

expect(__).toBe(triple(4), "what is triple 4?");

});

it("self invoking functions", function () {

let publicValue = "shared";

// self invoking functions are used to provide scoping and to alias letiables

(function (pv) {

let secretValue = "password";

expect(__).toBe(pv, "what is the value of pv?");

expect("__").toBe(

typeof secretValue,

"is secretValue available in this context?"

);

expect("__").toBe(

typeof publicValue,

"is publicValue available in this context?"

);

})(publicValue);

expect("__").toBe(

typeof secretValue,

"is secretValue available in this context?"

);

expect("__").toBe(

typeof publicValue,

"is publicValue available in this context?"

);

});

it("arguments array", function () {

let add = function () {

let total = 0;

for (let i = 0; i < arguments.length; i++) {

// complete the implementation of this method so that it returns the sum of its arguments

// __

}

// __

};

expect(15).toEqual(add(1, 2, 3, 4, 5), "add 1,2,3,4,5");

expect(9).toEqual(add(4, 7, -2), "add 4,7,-2");

});

it("using call to invoke function", function () {

let invokee = function (message) {

return this + message;

};

//another way to invoke a function is to use the call function which allows

//you to set the callers "this" context. Call can take any number of arguments:

//the first one is always the context that this should be set to in the called

//function, and the arguments to be sent to the function,multiple arguments are separated by commas.

let result = invokee.call("I am this!", "Where did it come from?");

expect(__).toBe(result, "what will the value of invokee's this be?");

});

it("using apply to invoke function", function () {

let invokee = function (message1, message2) {

return this + message1 + message2;

};

//similar to the call function is the apply function. Apply only has two

//arguments: the first is the context that this should be set to in the called

//function and the second is the array of arguments to be passed into the called function.

let result = invokee.apply("I am this!", ["I am arg1", "I am arg2"]);

expect(__).toBe(result, "what will the value of invokee's this be?");

});

});