pattern match in js

elixir.js

// https://elixir-lang.org/getting-started/case-cond-and-if.html#case

function elixir(...conds) {
    function arrayEqualsCond(a, b) {
        if (a.length !== b.length) {
            return false;
        }
        let eq = true;
        for (let i = 0; i < a.length; i++) {
            if (a[i] !== b[i] && !(b[i] instanceof Matcher)) {
                eq = false;
            }
        }
        return eq;
    }

    class Matcher {
        constructor(conds) {
            this.conds = conds;
        }

        when(...exp) {
            return {
                then: value => {
                    // console.log(this.conds, exp);
                    if (arrayEqualsCond(this.conds, exp)) {
                        this.value = value;
                    }
                }
            };
        }

        else(value) {
            if (this.value === undefined) {
                this.value = value;
            }
        }
    }

    class ElixirCase {
        constructor(conds) {
            this.conds = conds;
        }

        do(callback) {
            const matcher = new Matcher(this.conds);
            callback(matcher);
            return matcher.value;
        }
    }

    return new ElixirCase(conds);
}

const res = elixir(1, 2, 4).do(_ => {
  _.when(4, 5, 6).then("This clause won't match");
  _.when(1, _, 3).then("This clause will match and binded to _.value");
  _.else("Nothing hit");
});

console.log(res); // => "This clause will match and binded to _.value"