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.
npm install conditional-expression --save
Without ES6:
var match = require('conditional-expression').default;
match(1)
.equals(1).then(function () {
console.log('hello world');
}).else(false);
With ES6:
import match from 'conditional-expression';
match(1)
.equals(1).then(() => console.log('hello world'))
.else(false);
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');
// or
match('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'
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.
Evaluates as true based on passed regular expression.
match(73)
.with(/[0-9]/).then(true)
.else(false);
// returns true
Evaluates as true based on strict equality ===.
match('tortoise')
.equals('tortoise').then(true)
.else(false);
// returns true
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
Evaluates as true based a type.
match({})
.typeOf('object').then(true)
.else(false);
// returns true
Evaluates as true based on sizes.
match(2).greaterThan(1).then(true).else(false);
// returns true
match('ab').lessThan('abc').then(true).else(false);
// returns true
match(2).atLeast(2).then(true).else(false);
// returns true
match(2).atLeast(1).then(true).else(false);
// returns true
match(2).atMost(2).then(true).else(false);
// returns true
match(2).atMost(1).then(true).else(false);
// returns true
You can use nested matching to create subbranches for evaluation. Only 1 level deep nest is directly supported using thenMatch function.
const param = '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.
const param = '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
- Fixed README
- Added greaterThan({}), lessThan({}), atLeast({}), atMost({}) for comparing sizes
- Fixed Node.js support
- 100 % test coverage provided.
- Matching now supports one level of nesting using "thenMatch" function.
- Added more assertion to test the package and new functionality.
- Changed the internal structure to promote more internal reusability of the code to add more matching functions in the future if needed.
- 100 % test coverage provided.
- "include" function to always returns false if matching over anything else than a string.
- 100 % test coverage provided.
- Initial version of conditional-expression providing matching without nesting using.
- 100 % test coverage provided.
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Find me on Medium: https://medium.com/@martinnovk_22870