conditional-expression

Providing 'match' function as a JavaScript functional conditional expression to replace conditional statements 'if' and 'switch' as an alternative to ternary operator expression.

GitHub repository: https://github.com/MartinGentleman/conditional-expression

Medium article explaining motivation and use for the package: How to replace switch and ternaries in functional JavaScript.

Install

npm install conditional-expression --save

Without ES6:

varmatch=require('conditional-expression').default;match(1).equals(1).then(function(){console.log('hello world');}).else(false);

With ES6:

importmatchfrom'conditional-expression';match(1).equals(1).then(()=>console.log('hello world')).else(false);

Usage

First you call match function on an expression that you want to match:

match('functional programming');

Next you choose how you want to match the expression by choosing appropriate matching function. For example:

match('functional programming').includes('programming');

You follow up by calling 'then' function to tell it what to do in case of a positive match. You can pass a simple value as well as a function that will be automatically evaluated:

match('something').with(/[a-z]/).then('awesome');// ormatch('functional programming').includes('programming').then(()=>console.log('awesome'));

You have the option of chaining:

match(42).typeOf('string').then('it is a string').equals('42').then('Answer to the Ultimate Question of Life, the Universe, and Everything');

And you finish everything by calling 'else' which is mandatory:

match('http://domain.tld').on(url=>url.substr(0,5)==='https').then('It is HTTPS indeed').else('It is not HTTPS and that makes me sad :(');// returns 'It is not HTTPS and that makes me sad :('

Once a match is found, no other matching is performed:

match('funny joke').equals('sad').then('I am false').with(/[a-z]/).then('I am true and I am the result').includes('joke').then('I am true but I am not evaluated').else('I just execute everything');// returns 'I am true and I am the result'

Matching functions

on({function})

Evaluates as true if passed function returns boolean true, every other result of a function evaluates as false. Given function is also passed the expression over which we are matching as a parameter.

match({grumpy: 'cat'}).on(x=>x.grumpy==='cat').then(true).else(false);// returns true

Internally this function is used to implement or other matching functions.

with({RegEx})

Evaluates as true based on passed regular expression.

match(73).with(/[0-9]/).then(true).else(false);// returns true

equals({*})

Evaluates as true based on strict equality ===.

match('tortoise').equals('tortoise').then(true).else(false);// returns true

includes({string})

Evaluates as true based on whether a substring is included. Always evaluates as false if not used to match on a string.

match('Martian').includes('arti').then(true).else(false);// returns true

typeOf({string})

Evaluates as true based a type.

match({}).typeOf('object').then(true).else(false);// returns true

greaterThan({}), lessThan({}), atLeast({}), atMost({})

Evaluates as true based on sizes.

match(2).greaterThan(1).then(true).else(false);// returns truematch('ab').lessThan('abc').then(true).else(false);// returns truematch(2).atLeast(2).then(true).else(false);// returns truematch(2).atLeast(1).then(true).else(false);// returns truematch(2).atMost(2).then(true).else(false);// returns truematch(2).atMost(1).then(true).else(false);// returns true

thenMatch() nested matching

You can use nested matching to create subbranches for evaluation. Only 1 level deep nest is directly supported using thenMatch function.

constparam='this is string';match(param).includes('this').thenMatch(param).includes('string').then(true).else(false);.else(false);// returns true

Notice that thenMatch uses its own parameter and that else in the nested branch is still required.

To support deeper branching, you can pass match evaluation as a parameter to then function.

constparam='this is string';match(param).includes('this').thenMatch(param).includes('is').then(()=>match(param).includes('string').then(true).else(false)).else(false);.else(false);// returns true