After reading the Jest documentation, when it's mentioned that to export a single function from a tested file they show the following example:
function sum(a, b) {
return a + b;
}
module.exports = sum;
Now, if I have multiple specific functions I want to export on my tested file, like this:
function sum(a, b) {
return a + b;
}
function multiply(a, b) {
return a * b;
}
function subtract(a, b) {
return a - b;
}
module.exports = sum;
module.exports = multiply;
The multiply function is the only one being exported. How can I make these function be exported? Or only part of my file?
You can do something like this :
module.exports = {};
module.exports.sum = function sum(a, b) {
return a + b;
}
module.exports.multiply = function multiply(a, b) {
return a * b;
}
module.exports.subtract = function subtract(a, b) {
return a - b;
}
End you use it like this:
var MyMathModule = require('./my_math_module');
MyMathModule.sum(a, b);
MyMathModule.multiply(a, b);
MyMathModule.subtract(a, b);
First, in your example, all you are doing there is overriding the exports object with a function ( which is totally fine )
The exports and module.exports are an object and are actually the same object ( i.e. module.exports === exports // true )
To do what you want you can do this a couple ways:
exports.sum = sum
exports.multiply = multiply
or
module.exports = { sum: sum, multiply: multiply } // etc
or
module.exports.sum = sum
module.exports.multiply = multiply
Having in mind the answer to this question, i'll paste here 2 ways to do the same thing.
For example, you have the JS file called exercise5, like this:
//You can create an object with functions, as follows:
const wordAnalysis = {
type: (word) => typeof (word),
whiteSpaces: (word) => {
let wordAnalysis = word.includes(' ')
if (wordAnalysis) {
return 'It has spaces'
} else {
return "It doesn't has spaces"
}
}
}
//Or you can create several single functions, like the following:
function numberAnalysis(word) {
let isANumber = typeof (word) === 'number' ? true : false
return isANumber
}
// în order to avoid overwriting the module.exports, it is needed to do one of the following (I chose the first one):
// 1)
module.exports.firstPlace = wordAnalysis
module.exports.secondPlace = numberAnalysis
// 2)
// module.exports = {
// functions: functions,
// isANumber: isANumber
// }
// 3)
// exports.functions = functions
// exports.isANumber = isANumber
// 4)
// exports = {
// functions: functions,
// isANumber: isANumber
// }
Now the file test named exercise5.test.js:
const wordAnalysis = require('./exercise5')
const numberAnalysis = require('./exercise5')
test('It should give me the type of what was typed', () => {
expect(wordAnalysis.firstPlace.type('teste')).toEqual('string')
})
test('It should give me the type of what was typed', () => {
expect(wordAnalysis.firstPlace.type(22)).toEqual('number')
})
test("It should give true if what is typed has at least a space or false if it doesn't", () => {
expect(wordAnalysis.firstPlace.whiteSpaces('Jon is cool')).toEqual('It has spaces');
})
test("It should give true if what is typed has at least a space or false if it doesn't", () => {
expect(wordAnalysis.firstPlace.whiteSpaces('AllTogetherNow')).toBe("It doesn't has spaces");
})
test('it should analyse if the given expression is a number or not', () => {
expect(numberAnalysis.secondPlace(2)).toBeTruthy()
})
test('it should analyse if the given expression is a number or not', () => {
expect(numberAnalysis.secondPlace('jon')).toBeFalsy()
})
The only thing you need to be aware is to export/import the correct object/function, and of course call it when your are developing the test.
Related
I'm working on a pet project, a little front-end library for students. It reads variables/code in a JS file and tests it, outputting some panels. The code itself roughly follows the Jest framework.
My problem is that I'm trying to create a function that watches the execution of other functions, counts them, and lets me access the count.
function watchFunction(funcName){
let originalFunction = window[funcName];
let counter = 0;
// Wrap the function, counts when called
window[funcName] = function(...args){
console.log("watching");
counter++;
return originalFunction(...args);
}
return {
getCount: () => {return counter},
reset: () => {
// Unwrap the function
window[funcName] = originalFunction
}
}
}
This seems to work for methods like Number() or parseInt(), but I don't know how I would go about accessing methods like Math.floor(), or prototype methods like Array.prototype.map().
I've tried passing in the function reference instead of using window["funcNameString"], but that doesn't seem to work.
Does anyone have suggestions or tips for wrapping functions or watching functions like this?
EDIT:
It appears a solution was found!
function watchFunction(obj, fName) {
let counter = 0;
const originalFunction = obj[fName];
obj[fName] = (...args) => {
counter++;
return originalFunction.bind(obj)(...args);
};
return {
removeWatcher: () => (obj[fName] = originalFunction),
resetCount: () => (counter = 0),
getCount: () => counter,
};
}
Example of use:
// Array.prototype.push
const arrayPushWatcher = watchFunction(Array.prototype, "push");
let arr = [];
// 0
console.log("Array.prototype.push", arrayPushWatcher.getCount());
arr.push(1);
// 1
console.log("Array.prototype.push", arrayPushWatcher.getCount());
arr.push(1);
// 2
console.log("Array.prototype.push", arrayPushWatcher.getCount());
arrayPushWatcher.removeWatcher();
arr.push(1);
// 2 (stopped counting)
console.log("Array.prototype.push", arrayPushWatcher.getCount());
How to watch for any function call
Is that what you want? I can also write a block for this function so that it determines whether an object has been passed in or a string. If string -> run this function on window as a property "objectThatStoresFunction".
I've tried playing around with the Function.prototype, but it doesn't really work. So the function turned out a bit more complex.
This code below works both with functions / objects on window Array.prototype.map (Prototype / Class functions)
function watchFunction(objectThatStoresFunction, functionName) {
let counter = 0;
const originalFunction = objectThatStoresFunction[functionName];
objectThatStoresFunction[functionName] = (...args) => {
counter += 1;
return originalFunction(...args);
}
return {
getCount: () => {
return counter
}
}
}
const mathRoundWatcher = watchFunction(Math, 'round');
// 0
console.log(mathRoundWatcher.getCount());
// 1
Math.round(99666.9999999);
console.log(mathRoundWatcher.getCount());
// 2
Math.round(999999999.99);
console.log(mathRoundWatcher.getCount());
function watchFunction(objectThatStoresFunction, functionName, optionalOriginalFunction) {
const self = this;
if (optionalOriginalFunction) {
objectThatStoresFunction = this.window;
functionName = optionalOriginalFunction.name;
}
let counter = 0;
const originalFunction = objectThatStoresFunction[functionName] || optionalOriginalFunction;
objectThatStoresFunction[functionName] = (...args) => {
counter += 1;
return originalFunction.bind(self)(...args);
}
return {
// should it remove the watcher or reset the count?
reset: () => objectThatStoresFunction[functionName] = originalFunction,
getCount: () => {
return counter;
}
}
}
const arrayMapWatcher = watchFunction(Array.prototype, 'map');
// 0
console.log('Array.prototype.map', arrayMapWatcher.getCount());
[-99].map(() => {});
// 1
console.log('Array.prototype.map', arrayMapWatcher.getCount());
const mathRoundWatcher = watchFunction(Math, 'round');
// 0
console.log('Math.round', mathRoundWatcher.getCount());
// 1
Math.round(99666.9999999);
console.log('Math.round', mathRoundWatcher.getCount());
// 2
Math.round(999999999.99);
console.log('Math.round', mathRoundWatcher.getCount());
const alertWatcher = watchFunction(null, null, window.alert);
// 0
console.log('window.alert', alertWatcher.getCount());
// 1
window.alert('1');
console.log('window.alert', alertWatcher.getCount());
// 2
alert('2')
console.log('window.alert', alertWatcher.getCount());
// reset the alertWatcher counter
alertWatcher.reset();
This code above breaks the stacksnippets.com when used with Array.prototype.map for some reason, please see this JsFiddle link:
https://jsfiddle.net/ctbjnawz/3/
Do you mean a method of an instance or object? One way is to create a new function. e.g
function WatchInstanceMethods(instance, functionName){
let originalFunction = window[instance][funcName];
let counter = 0;
window[instance][functionName] = function(...args){
console.log("watching");
counter++;
return originalFunction(...args);
}
return {
getCount: () => {return counter},
reset: () => {
// Unwrap the function
window[funcName] = originalFunction
}
}
}
although adding support for chaining methods will get difficult with more nested methods but you can pass a string for functionName name and split it to have each layer of calling instance for function and repeat the logic above.
I got asked this in an Interview and I couldn't solve it. Was wondering if any of you guys can help me.
fn("hello").fn("world").fn("!!!").fn();
function fn (str){
// Enter Solution Here
}
The solution should return 'hello world !!!'.
I tried method chaining and was able to get a partially right answer which is as follows:
function fn(str) {
var string = str;
this.fn1 = function(str1) {
string += " "+str1;
return this;
}
this.fn = function() {
console.log(string)
}
}
new fn("hello").fn1("world").fn1("!!!").fn();
but as you can see I cant get it to work unless I use fn1 as the function to concat the string. Any help will be appreciated, thanks.
Have the function return an object with one fn method. If, when you call it, it has an argument, update the string, otherwise return the string so you can log it.
function fn(str = '') {
return {
fn: function (s) {
if (s) {
str += ` ${s}`;
return this;
}
return str;
}
};
}
const output = fn('hello').fn('world').fn('!!!').fn();
console.log(output);
Additional documentation
Template/string literals
You could return an object with two properties, one for returning the complete string and another for collecting parts and retuning the object.
function fn(str) {
const
fns = {
fn: function () {
return str;
},
fn1: function (s) {
str += ' ' + s;
return fns;
}
};
return fns;
}
console.log(fn("hello").fn1("world").fn1("!!!").fn());
I think this should do the trick:
function fn(s){
return new function(){
this.str = s;
this.fn = (ns) => {if(ns){this.str += " "+ns; return this;} else return this.str;};
}
}
let a = fn("hello").fn("world").fn("!!!").fn();
console.log(a);
Seems like you need to use objects
const generic = {
"fn1":null,
"current":"",
"fn": () => {
//what do you want to do with "this.current"?
}
}
function fn(str) {
var ret = generic;
ret.fn1 = (wa) =>{
var again = generic;
again.current +=wa;
return again;
}
ret.current += str;
return ret;
}
You can return an object with a .fn() method which will
check if an argument is passed in or not to determine when to terminate the chain or continue chaining.
When no argument is sent, then it simply returns the accumulated string.
Otherwise, it calls fn() function again to accumulate to the string and get the next copy of the same structure as before:
const result = fn("hello").fn("world").fn("!!!").fn();
console.log(result);
function fn (str){
return {
fn(nextString) {
if (nextString === undefined)
return str;
return fn(`${str} ${nextString}`);
}
};
}
Since this operation is immutable, it means each link in the chain is independent, therefore it is no problem with assigning to variables to continue with different chains:
const helloWorld = fn("hello").fn("world");
const one = helloWorld.fn("one").fn();
const two = helloWorld.fn("two").fn();
const three = helloWorld.fn("three").fn();
console.log(one);
console.log(two);
console.log(three);
function fn (str){
return {
fn(nextString) {
if (nextString === undefined)
return str;
return fn(`${str} ${nextString}`);
}
};
}
I have a module that I'm exporting. I need one function to call another function. Here's a simplified version of what I'm trying to do.
module.exports = {
isEven: (number) => {
return (number%2 == 0)
},
isTenEven: () => {
return isEven(10)
}
}
The code above throws isEven is not defined when moduleName.isTenEven() is called.
It makes sense why it fails. But how would you rewrite it? (While maintaining the singleton pattern)
Define the functions first, then export them:
const isEven = (number) => number % 2 === 0
const isTenEven = () => isEven(10)
module.exports = {
isEven,
isTenEven
}
The object is only used to group the functions together. There's nothing really OO about it so define the functions separately. Construct the object at the end.
const isEven = number => number % 2 === 0;
const isTenEven = () => isEven(10);
module.exports = { isEven, isTenEven };
Maybe just do this? Define then export.
const isEven = number => number % 2 === 0;
module.exports = {
isEven,
isTenEven: () => isEven(10)
};
Just to add one more solution to the mix. You don't have to define the function elsewhere. Since the object declaration is complete before the function gets called, you can refer to it via module.exports or via exports like this:
module.exports = exports = {
isEven: (number) => {
return (number%2 === 0)
},
isTenEven: () => {
return exports.isEven(10)
}
}
If you were doing this in a lot of methods, you could define a shorter variable name for the exported object and refer to it.
If you can afford Babel or a version of Node.js that supports import/export statements you could also do:
export const isEven = num => num % 2 === 0;
export const isTenEven = () => isEven(10);
Inside JS object literal using this refers to the object itself so you can have:
module.exports = {
isEven: (number) => {
return (number%2 == 0)
},
isTenEven: function () {
return this.isEven(10)
}
}
I have multiple observables that I want to chain with the concat observable. But what I need is the same behavior like compose, b needs to get the results of a and c the results of b.
function a(observable) { return observable.map()... }
function b(observable) { return observable.map()... }
function c(observable) { return observable.map()... }
const obs = Observable.of([...])
Observable.concat(a(obs), b(obs), c(obs)).subscribe(...)
How can I do this?
As far as I know Rx does not have helper for composing function. However, is this what you was looking for?
function a(source$) {
return source$.map(x => x + '-first')
}
function b(source$) {
return source$.map(x => x + '-second')
}
function c(source$) {
return source$.map(x => x + '-third')
}
const composed = R.compose(c, b, a);
composed(Rx.Observable.interval(1000))
.subscribe(val => {
console.log(val);
});
<script src="https://unpkg.com/#reactivex/rxjs#5.0.3/dist/global/Rx.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.22.1/ramda.min.js"></script>
is there a way to test multiple functions in one file with jest?
in ch03.js:
var min = function(a, b) {
if(a < b)
return a
else
return b
}
// even/odd number checker
var isEven = function(number) {
n = Math.abs(number);
if (n==0)
return true;
else if (n==1)
return false;
else {
return isEven(n-2);
}
}
module.exports = isEven;
and my test file:
in test/ch03-test.js
jest.dontMock('../ch03');
describe('min', function() {
it('returns the minimum of two numbers', function() {
var min = require('../ch03');
expect(min(2, 3)).toBe(2);
expect(min(22, 3)).toBe(3);
expect(min(2, -3)).toBe(-3);
});
});
describe('isEven', function() {
it('checks if given number is even', function() {
var isEven = require('../ch03');
expect(isEven(0)).toBe(true);
expect(isEven(-2)).toBe(true);
expect(isEven(0)).toBe(true);
expect(isEven(3)).toBe(false);
});
});
I don't want separate files for every small javascript function.
Is there a way to test multiple functions in one file?
You should try rewire
When "requiring" a module with rewire, it exposes getter and setter for variables in the module, including private ones.
Something like this should work:
jest.dontMock('../ch03');
var rewire = require('rewire');
var min = rewire('../ch03').__get__("min");
describe('min', function() {
it('returns the minimum of two numbers', function() {
expect(min(2, 3)).toBe(2);
expect(min(22, 3)).toBe(3);
expect(min(2, -3)).toBe(-3);
});
});