Published Dec 04, 2019
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Composable factory functions represents a particular type of factory function that can be “composed” together to build new enhanced functions. They are especially useful for allowing us to construct objects that “inherit” behaviors and properties from different sources without the need for building complex class hierarchies.
Let’s assume we want to build a video game in which the characters on the screen can have a number of different behaviors: they can move on the screen; they can slash and shoot. And yes, to be a character they should have some basic properties such as life points, position on the screen, and name.
We want to define several types of character, one for every specific behavior:
Ideally we would be able to define new types of characters, combining different behaviors from the existing ones, We want absolute freedom and, for example, we would like to define these new types on top of the existing ones:
As you can see, we want total freedom in combining the features of every basic type, so it should be obvious that we cannot easily model this problem using classes and inheritance.
const stampit = require('stampit')
const character = stampit().props({
name: 'anonymous',
lifePoints: 100,
x: 0,
y: 0
})
const c = character();
c.name = 'John'
c.lifePoints = 10;
const mover = stampit().methods({
move(xIncr, yIncr) {
this.x += xIncr
this.y += xIncr
console.log(`${this.name} moved to [${this.x}, ${this.y}]`)
}
})
const slasher = stampit().methods({
slash(direction){
console.log(`${this.name} slashed to the ${direction}`)
}
})
const shooter = stampit().props({bullets: 6}).methods({
shoot(direction){
if(this.bullets > 0){
--this.bullets;
console.log(`${this.name} shoot to the ${direction}`)
}
}
})
const runner = stampit.compose(character, mover)
const samurai = stampit.compose(character, mover, slasher)
const sniper = stampit.compose(character, shooter)
const gunslinger = stampit.compose(character, mover, shooter)
const westernSamurai = stampit.compose(gunslinger, samurai)
const gojiro = westernSamurai()
gojiro.name = 'Gojiro Kiryu'
gojiro.slash('left')
gojiro.shoot('right')