For Redux, you cannot use mutable methods like push, splice. Need to use immutable methods such as concat, slice and ...spread

Html:

<!DOCTYPE html>

<html>

<head>

  <meta charset="utf-8">

  <title>JS Bin</title>

  <script src="https://wzrd.in/standalone/expect@latest"></script>

  <script src="https://wzrd.in/standalone/deep-freeze@latest"></script>

</head>

<body>

</body>

</html>

push() vs concat()

push: modify the array;

concat: return a new array;

console.clear();

const addCounter = (list)=>{

  list.push(0);

  return list;

}

const testAddCounter = ()=>{

  const beforeList = [];

  const afterList = [0];

  deepFreeze(beforeList);

  expect(

    addCounter(beforeList)

  ).toEqual(afterList);

}

testAddCounter();

console.log("All tests passing..");

/**

"error"

"TypeError: Can't add property 0, object is not extensible

    at addCounter (fegewebemu.js:5:8)

    at testAddCounter (fegewebemu.js:15:10)

    at fegewebemu.js:18:1"

*/

console.clear();

const addCounter = (list)=>{

  let res = list.concat(0);

  return res;

}

const testAddCounter = ()=>{

  const beforeList = [];

  const afterList = [0];

  deepFreeze(beforeList);

  expect(

    addCounter(beforeList)

  ).toEqual(afterList);

}

testAddCounter();

console.log("All tests passing..");  // passing

Using ...spread:

console.clear();

const addCounter = (list)=>{

  return [...list, 0];

}

const testAddCounter = ()=>{

  const beforeList = [];

  const afterList = [0];

  deepFreeze(beforeList);

  expect(

    addCounter(beforeList)

  ).toEqual(afterList);

}

testAddCounter();

console.log("All tests passing.."); // Passing

splice() vs slice()

splice: modfiy array;

slices: return new array;

console.clear();

const removeCounter= (list, index)=>{

   list.splice(index, 1);

  return list;

}

const testRemoveCounter = ()=>{

  const beforeList = [0 ,10,20];

  const afterList = [0, 20];

  deepFreeze(beforeList);

  expect(

    removeCounter(beforeList, 1)

  ).toEqual(afterList);

}

testRemoveCounter();

console.log("All tests passing.."); 

/**

"error"

"TypeError: Cannot add/remove sealed array elements

    at removeCounter (fegewebemu.js:5:8)

    at testRemoveCounter (fegewebemu.js:15:10)

    at fegewebemu.js:17:1"

*/

console.clear();

const removeCounter= (list, index)=>{

  return list.slice(0, index)

  .concat(list.slice(index+1));

}

const testRemoveCounter = ()=>{

  const beforeList = [0 ,10,20];

  const afterList = [0, 20];

  deepFreeze(beforeList);

  expect(

    removeCounter(beforeList, 1)

  ).toEqual(afterList);

}

testRemoveCounter();

console.log("All tests passing.."); // Passing

ES6:

console.clear();

const removeCounter= (list, index)=>{

  return [

    ...list.slice(0, index),

    ....list.slice(index + 1)

  ];

}

const testRemoveCounter = ()=>{

  const beforeList = [0 ,10,20];

  const afterList = [0, 20];

  deepFreeze(beforeList);

  expect(

    removeCounter(beforeList, 1)

  ).toEqual(afterList);

}

testRemoveCounter();

console.log("All tests passing.."); // Passing

Modify one element in array:

console.clear();

const incrementCounter = (list, index) => {

   list[index]++;

  return list;

};

const testIncrementCounter = ()=>{

  const beforeList = [0 ,10,20];

  const afterList = [0, 11, 20];

  deepFreeze(beforeList);

  expect(

    incrementCounter(beforeList, 1)

  ).toEqual(afterList);

}

testIncrementCounter();

console.log("All tests passing..");

/**

"error"

"Error: Expected [ 0, 10, 20 ] to equal [ 0, 11, 20 ]

    at Object.assert [as default] (https://wzrd.in/standalone/expect@latest:489:9)

    at Expectation.toEqual (https://wzrd.in/standalone/expect@latest:70:26)

    at testIncrementCounter (fegewebemu.js:16:43)

    at fegewebemu.js:18:1"

*/

console.clear();

const incrementCounter = (list, index) => {

   let res = list.slice(0, index)

     .concat(++list[index])

     .concat(list.slice(index+1));

  return res;

};

const testIncrementCounter = ()=>{

  const beforeList = [0 ,10,20];

  const afterList = [0, 11, 20];

  deepFreeze(beforeList);

  expect(

    incrementCounter(beforeList, 1)

  ).toEqual(afterList);

}

testIncrementCounter();

console.log("All tests passing.."); // Passing

ES6:

console.clear();

const incrementCounter = (list, index) => {

   return [

     ...list.slice(0, index),

     ++list[index],

     ...list.slice(index+1)

   ];

};

const testIncrementCounter = ()=>{

  const beforeList = [0 ,10,20];

  const afterList = [0, 11, 20];

  deepFreeze(beforeList);

  expect(

    incrementCounter(beforeList, 1)

  ).toEqual(afterList);

}

testIncrementCounter();

console.log("All tests passing.."); // Passing

[Redux] Avoiding Array Mutations with concat(), slice(), and ...spread的更多相关文章

  1. [Redux] Avoiding Object Mutations with Object.assign() and ...spread

    Learn how to use Object.assign() and the spread operator proposed for ES7 to avoid mutating objects. ...

  2. 数组方法concat & slice

    掌握数组的操作方法: concat() /  slice() concat() 语法: arrayObject.concat(arrayX,arrayY,....,arrayZ) 功能:用于连接两个或 ...

  3. 【译】Rust中的array、vector和slice

    原文链接:https://hashrust.com/blog/arrays-vectors-and-slices-in-rust/ 原文标题:Arrays, vectors and slices in ...

  4. [Javascript] Array methods in depth - slice

    Array slice creates a shallow copy of an array. In this lesson we cover, in detail, exactly what a ' ...

  5. JavaScript引用类型之Array数组的concat()和push()方法的区别

    在javascript中,我们一般都只用push向数组的尾部插入新元素的,但是其实在javascript中还有另外一个方法和push一样,也是向数组尾部插入新元素的,但是他们之间却存在着一定的区别,当 ...

  6. (转)Array.prototype.slice.call自解

    很多框架或者库里面都会有这句的使用,最多的还是通过Array.prototype.slice.call(arguments,0)把arguments这个伪数组转换为真正的数组.但为什么可以这么做,却一 ...

  7. 【Go入门教程2】内置基础类型（Boolean、数值、字符串、错误类型），分组，iota枚举，array（数值），slice（切片），map（字典），make/new操作，零值

    这小节我们将要介绍如何定义变量.常量.Go内置类型以及Go程序设计中的一些技巧. 定义变量 Go语言里面定义变量有多种方式. 使用var关键字是Go最基本的定义变量方式,与C语言不同的是Go把变量类型 ...

  8. 【GoLang】GoLang 遍历 map、slice、array方法

    代码示例: map1 := make(map[string]string) map1["a"] = "AAA" map1["b"] = &q ...

  9. 详解 Array.prototype.slice.call(arguments)

    首先,slice有两个用法,一个是String.slice,一个是Array.slice,第一个返回的是字符串,第二个返回的是数组 在这里我们看第二个方法 1.在JS里Array是一个类 slice是 ...

随机推荐

  1. Linux下登陆mysql服务器不需要输入账号密码信息

    linux下登录mysql服务器一般都是在命令行手动输入链接信息 [root@localhost ~]# mysql -hlocalhost -uroot -p11111 而在mysql 5.6之后版 ...

  2. 集成支付宝后出现LaunchServices: ERROR: There is no registered handler for URL scheme alipay

    原因如下: There's no problem with your implementation. All those warnings mean is the apps which each UR ...

  3. 三、singleton(单例化)一个对象的几种方法

    方案一:私有化构造器,通过static final域 @Test public void test13() { A215 a=A215.a; A215 b=A215.a; System.out.pri ...

  4. PHP后台传值

    前台数据往后台传值,往往是新手最头痛的,最近在学习thinkPHP的时候,也遇到了这种问题,总结一下,往不足之处请大家指教. 一.前台界面代码,往后台传值有两种方式,一种是get,另一种是post,新 ...

  5. cocos2dx lua调用C++类.

    最近需求所迫, 终于着手传说中的 lua 了. 折腾了4天, 总算大概搞明白了用法. 细节咱们就别谈了, 直接说项目里怎么跑起来. 准备工作 我们需要一系列繁琐的前奏. tolua++: 这是必备工具 ...

  6. 关于auto和decltype

    auto会忽略顶层const,保留底层const ; const int* const p = &i; auto p2 = p; //p2是const int*,不是const int* co ...

  7. Zsh安装CMake补全脚本进行CMake命令补全

    最近在尝试使用Zsh,发现其补全命令的功能相当厉害.但对CMake命令的补全在默认的5.0.5中好像没有看到,网上找了下关于配置Zsh补全的文章也没有多少.     于是自己动手,发现在Zsh安装目录 ...

  8. （转载）用css来实现十字的布局

    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/ ...

  9. 每日一算法【one】

    //有一个数组  {1,2,3,4,5,6,7,8,9,12,13,45,67,89,99,101,111,123,134,565,677} 查找数组中是否有指定的某一个数. /** *------- ...

  10. [转] .NET 3.5中MSChart组件的ImageLocation属性含义

    在.NET程序/网站中如果要生成统计图表/图形,以前可以采用OWC(Office Web Components),如OfficeXP组件OWC10.Office2003组件OWC11.OWC采用COM ...