ArkTS Performant Programming Practices

Overview

This topic provides a set of performant programming practices that you can apply in performance-critical scenarios. They are techniques and recommendations drawn from real-world development. Following these practices in your service implementation can help develop performant applications. For details about ArkTS programming specifications, see ArkTS Coding Style Guide.

Declarations and Expressions

Using const to Declare Unchanged Variables

You are advised to use const to declare variables that remain unchanged.

const index = 10000; // This variable does not change in the subsequent process. You are advised to declare it as a constant.

Avoiding Mixed Use of Integers and Floating-Point Numbers in Variables of the number Type

For variables of the number type, integer data and floating-point data are distinguished during optimization at runtime. As such, avoid changing the data type of the variables after they have been initialized.

let intNum = 1;
intNum = 1.1; // This variable is declared as an integer data type. Avoid assigning a floating-point number to it.

let doubleNum = 1.1;
doubleNum = 1; // This variable is declared as a floating-point data type. Avoid assigning an integer to it.

Avoiding Overflow in Arithmetic Operations

When arithmetic operations run into overflow, the engine enters a slower logic branch for processing overflow, affecting subsequent performance. Below are some suggestions to mitigate the overflow risk.

• For operations such as addition, subtraction, multiplication, and exponentiation, the value should not be greater than INT32_MAX (2147483647) or less than INT32_MIN (-2147483648).

• For operations such as & (and) and >>> (unsigned right shift), the value should not be greater than INT32_MAX.

Extracting Constants in Loops to Reduce Attribute Access Times

If the constants do not change in the loop, they can be extracted outside the loop to reduce the number of access times.

class Time {
  static start: number = 0;
  static info: number[] = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12];
}

function getNum(num: number): number {
  let total: number = 348;
  for (let index: number = 0x8000; index > 0x8; index >>= 1) {
    // The system searches for info and start of Time multiple times, and the values found each time are the same.
    total += ((Time.info[num - Time.start] & index) !== 0) ? 1 : 0;
  }
  return total;
}

You can extract Time.info[num - Time.start] as a constant to reduce the number of attribute access times and improves performance. The optimized code is as follows.

class TimeBetter {
  static start: number = 0;
  static info: number[] = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12];
}

function getNumBetter(num: number): number {
  let total: number = 348;
  const info = TimeBetter.info[num - TimeBetter.start]; // Extract constants from the loop.
  for (let index: number = 0x8000; index > 0x8; index >>= 1) {
    if ((info & index) != 0) {
      total++;
    }
  }
  return total;
}

Functions

Using Parameters to Pass External Variables

Using closures may cause extra overhead.

let arr = [0, 1, 2];

function fooWithout(): number {
  return arr[0] + arr[1];
}

fooWithout();

In performance-sensitive scenarios, you are advised to pass external variables using parameters.

let arr_ = [0, 1, 2];

function fooWithArray(array: number[]): number {
  return array[0] + array[1];
}

fooWithArray(arr_);

Avoiding Optional Parameters

An optional function parameter may be undefined. When such a parameter is used in the function, the system needs to check whether the parameter is null, which will cause extra overhead.

function add(left?: number, right?: number): number | undefined {
  if (left != undefined && right != undefined) {
    return left + right;
  }
  return undefined;
}

Declare function parameters as mandatory parameters based on service requirements. You can use the default parameters.

function addWithParams(left: number = 0, right: number = 0): number {
  return left + right;
}

Arrays

Prioritizing TypedArray for Value Arrays

Where only arithmetic operations are involved, use TypedArray.

Sample code before optimization:

const arr1 = new Array<number>(1, 2, 3);
const arr2 = new Array<number>(4, 5, 6);
let res = new Array<number>(3);
for (let i = 0; i < 3; i++) {
  res[i] = arr1[i] + arr2[i];
}

Sample code after optimization:

const typedArray1 = Int8Array.from([1, 2, 3]);
const typedArray2 = Int8Array.from([4, 5, 6]);
let res1 = new Array<number>(3);
for (let i = 0; i < 3; i++) {
  res1[i] = typedArray1[i] + typedArray2[i];
}

Avoiding Sparse Arrays

When allocating an array whose size exceeds 1024 bytes or a sparse array during runtime, a hash table is used to store elements. This mode results in slower access speeds. Therefore, you should avoid converting arrays to sparse arrays during code development.

// Allocate an array of 100,000 bytes, for which a hash table is used to store elements.
let count = 100000;
let res: number[] = new Array(count).fill(0);

// The array will become a sparse array when the value is changed to 9999 after the array is created.
let result: number[] = [];
result[9999] = 0;

Avoiding Arrays of Union Types

When appropriate, use arrays that contain elements of the same type. That is, avoid using arrays of union types. Avoid mixed use of integer data and floating-point data in number arrays.

let arrNum: number[] = [1, 1.1, 2]; // Integer and floating-point data are mixed in the numeric array.
let arrUnion: (number | string)[] = [1, 'hello'];  // Union array.

Place the data of the same type in the same array based on service requirements.

let arrInt: number[] = [1, 2, 3];
let arrDouble: number[] = [0.1, 0.2, 0.3];
let arrString: string[] = ['hello', 'world'];

Exceptions

Avoiding Frequent Exceptions

Creating exceptions involves constructing the stack frame for the exception, which may incur performance overhead. In light of this, avoid frequently throwing exceptions in performance-sensitive scenarios, for example, in for loop statements.

Sample code before optimization:

function div(a: number, b: number): number {
  if (a <= 0 || b <= 0) {
    throw new Error('Invalid numbers.');
  }
  return a / b;
}

function sum(num: number): number {
  let sum = 0;
  try {
    for (let t = 1; t < 100; t++) {
      sum += div(t, num);
    }
  } catch (e) {
    console.info(e.message);
  }
  return sum;
}

Sample code after optimization:

function sumBetter(num: number): number {
  let sum = 0;
  for (let t = 1; t < 100; t++) {
    // Intercept exceptions directly to avoid frequent exceptions.
    if (num <= 0) {
      console.info('Invalid numbers.');
    }
    sum += divBetter(t, num);
  }
  return sum;
}