put.js

var addListener = require("./add-listener.js")
var setNonEnumerable = require("./lib/set-non-enumerable.js");

module.exports = put

// `obs.put` is a mutable implementation of `array[index] = value`
// that mutates both `list` and the internal `valueList` that
// is the current value of `obs` itself
function put(index, value) {
    var obs = this
    var valueList = obs().slice()

    var originalLength = valueList.length
    valueList[index] = typeof value === "function" ? value() : value

    obs._list[index] = value

    // remove past value listener if was observ
    var removeListener = obs._removeListeners[index]
    if (removeListener){
        removeListener()
    }

    // add listener to value if observ
    obs._removeListeners[index] = typeof value === "function" ?
        addListener(obs, value) :
        null

    // fake splice diff
    var valueArgs = index < originalLength ? 
        [index, 1, valueList[index]] :
        [index, 0, valueList[index]]

    setNonEnumerable(valueList, "_diff", [valueArgs])

    obs._observSet(valueList)
    return value
}