SMA implementation in simple function form, or in class form.

sma.js

// Simple move average
function sma(data, dataLength, sampleRate=250, frequency=50) {
    if (data.length === 0) return data;
    const filterTL = Math.round(sampleRate / frequency)
    const filteredData = []
    if (filterTL > dataLength) {
        throw new Error('Data length is not enough.')
    }
    else {
        for (let i = 0; i < dataLength; ++i) {
            if (i <= dataLength - filterTL) {
                let sum = 0
                for (let j = i; j < i + filterTL; ++j) {
                    sum += data[j]
                }
                const average = sum / filterTL
                filteredData.push(average)
            }
            else {
                filteredData.push(0) // Not necessary, maybe.
            }
        }
        return filteredData
    }
}

class SMACalculator {
    constructor(sampleRate = 250, frequency = 50) {
        this.container = []
        this.sampleRate = sampleRate
        this.frequency = frequency
        this.batchSize = Math.round(sampleRate / frequency)
        this.lastValue = null
        this.sum = null
    }

    update(newData = []) {
        console.log(`this.container length: ${this.container.length}`, this.container)
        const tempArray = this.container.concat(newData)
        const dataLength = tempArray.length
        const maxMoveIndex = dataLength - this.batchSize
        console.log(`maxMoveIndex: ${maxMoveIndex}`)
        // 如果传入的数组成员数不足，则存入容器，返回空数组
        if (dataLength < this.batchSize) {
            this.container = tempArray
            return []
        }
        // 开始移动。
        const result = []
        this.container = [] // 清空缓存
        for (let i = 0; i < dataLength; ++i) {
            // 计算移动平均值
            if (i <= maxMoveIndex) {
                // 计算 sum。
                if (this.sum === null) { // 第一次进入，先算出 sum 的初始值
                    for (let j = 0; j < this.batchSize; ++j) {
                        this.sum += tempArray[j]
                    }
                }
                else {
                    // 非第一轮运算时，当 i 为 0 时，调用缓存的 lastValue，否则直接用前一个值。
                    const lastValue = (i === 0) ? this.lastValue : tempArray[i-1]
                    console.log(`lastValue: ${lastValue}`)
                    this.sum = this.sum - lastValue + tempArray[i + this.batchSize - 1]
                }
                const average = this.sum / this.batchSize
                result.push(average) // 推入平均值

                // 存下参与计算的最后一个值
                if (i === maxMoveIndex) {
                    this.lastValue = tempArray[i]
               }
            }
            else {
                this.container.push(tempArray[i]) //缓存未参与运算的值
            }
        }
        return result
    }

    reset() {
        this.container = []
        this.lastValue = null
        this.sum = null
    }
}


const orig = [97,72,98,83,71,99,90,28,98,58,49,4,98,78,1,63,85,92,56,96,17,59,38,34,21,97,76,86,87,99,98,2,11,96,91,14,19,19,38]

const orig1 = [97,72,98,83,71,99,90,28]
const orig2 = [98,58,49,4,98,78,1,63,85,92,56,96]
const orig3 = [17,59,38,34,21,97,76,86,87,99,98,2,11,96,91]
const orig4 = [14,19,19,38]

const calc = new SMACalculator()
const result = calc.update(orig)

const calc2 = new SMACalculator()
const result2 = calc2.update(orig1).concat(calc2.update(orig2)).concat(calc2.update(orig3)).concat(calc2.update(orig4))

console.log(`orig: ${orig.length}`)
console.log(`Class: ${result}`, `${result.length}`)
console.log(`Class: ${result2}`, `${result2.length}`)
console.log(`Function: ${sma(orig, orig.length)}`, `${sma(orig, orig.length).length}`)


// const calc = new SMACalculator()
// let result = calc.update(orig1)
// console.log(`result: ${result.length}`, result)
// result = calc.update(orig2)
// console.log(`result: ${result.length}`, result)