Levelling up a user.

levelling-up.js

function attemptLevelUp(addedXp, currentXp, currentLevel) {
    var baseAmountForNextLevel = 0;

    for (i = 1; i <= currentLevel; i++) {
        baseAmountForNextLevel += xpNeededForNextLevel(i);
    }


    if ((currentXp + addedXp) >= baseAmountForNextLevel) {
        // I am levelling up.
        return {
            level: currentLevel + 1,
            totalXp: baseAmountForNextLevel,
            surplus: (currentXp + addedXp) - baseAmountForNextLevel
        }
    }

    // I am not levelling up.
    return {
        level: currentLevel,
        totalXp: currentXp + addedXp,
        surplus: 0
    }
}

function xpNeededForNextLevel(level) {
    var stepRange = Math.roundUp(level / 10) - 1;
    var stepModifier = stepRange * 0.5;

    return levelUpStepSize = (1 + stepModifier) * 1000;
}


var xp = 0;
var level = 1;
var added = 5000;

do {
    var result = attemptLevelUp(added, xp, level)

    if (result.surplus !== 0) {
        xp = result.totalXp;
        level = result.level;
        added: result.surplus;
    }
}
while(result.surplus !== 0);


// result.level === The users level.
// result.totalXp === The users total amount of XP after completion.