zoukankan      html  css  js  c++  java
  • [Javascript] Primitive value are immutable

    Primitive Values
    • Undefined (undefined), used for unintentionally missing values.
    • Null (null), used for intentionally missing values.
    • Booleans (true and false), used for logical operations.
    • Numbers (-1003.14, and others), used for math calculations.
    • Strings ("hello""abracadabra", and others), used for text.
    • Symbols (uncommon), used to hide implementation details.
    • BigInts (uncommon and new), used for math on big numbers.

    There is a old bug in Javascript which is typeof(null) === 'object', null is primitive value actually, but we have to live with this bug, fix it will break the world.

    Primitive are immutable!

    let reaction = 'yikes';
    reaction[0] = 'l';
    console.log(reaction);

    What's the output of console log?

    The Answer is:

    yikes

    In 'strict mode'; it will throw an error for that.

    A String is a primitive value, and that means a great deal! All primitive values are immutable. Which means it is unchangeable, read-only. You can't mess with primitive values. AT ALL!


    Variables are not values, Variable point to values

    let pet = 'Narwhal';
    pet = 'The Kraken';
    console.log(pet);

    What's the output again?

    The Answer is:

    // "The Kraken"

    But what about Primitive value are immutable? 

    Yes, but here, we assign to 'pet' variable. We can change 'pet' variable to "The Kraken".

  • 相关阅读:
    Centos7 Apache 2.4.18编译安装
    Centos7 mysql-community-5.7.11编译安装
    Centos7 安装MPlayer过程详解
    Vmware虚拟机克隆的网卡问题
    虚拟机VMware新增硬盘无法识别问题
    python推导式
    Python迭代器和生成器
    Python装饰器
    Python函数初识二
    Python函数初识
  • 原文地址:https://www.cnblogs.com/Answer1215/p/12327114.html
Copyright © 2011-2022 走看看