More Testable Code

more-testable-code.js

// BETTER - more testable
const incrementedVal = (val) => val + 1

function substituteVal(val, low, high) {
    if(val >= high) return high
    else if(val <= low) return low
    else return val
}
function shouldIncrement(val, disabled) {
    return val >= 0 && val < 10 && !disabled
}
function valIncrementer(val, disabled) {
    if( shouldIncrement(val, disabled) ) {
        return incrementedVal(val)
    }
    return substituteVal(val, 0, 10)
}