base1.nnb

{
    "cells": [
        {
            "language": "markdown",
            "source": [
                "# 兼容性 \n\n## Polyfill\n根据新特性的定义,实现在旧环境运行的等价功能。"
            ],
            "outputs": []
        },
        {
            "language": "typescript",
            "source": [
                "if (!Number.isNaN) {\n  Number.isNaN = function isNaN(x) {\n    return x !== x;\n  };\n}\n\nconsole.log(Number.isNaN(NaN));\n"
            ],
            "outputs": [
                {
                    "items": [
                        {
                            "mime": "application/vnd.code.notebook.stdout",
                            "value": [
                                "true",
                                ""
                            ]
                        }
                    ]
                }
            ]
        },
        {
            "language": "typescript",
            "source": [
                "if (!Object.is) {\n  Object.is = function (v1, v2) {\n    if (v1 === 0 && v2 === 0) {\n      return 1 / v1 === 1 / v2;\n    }\n    if (v1! == v1) {\n      return v2 !== v2;\n    }\n    return v1 === v2;\n  };\n}\n\nconsole.log(Object.is(NaN, NaN));\nconsole.log(Object.is(0, -0));\nconsole.log(Object.is(Infinity, 1 / 0));\n"
            ],
            "outputs": [
                {
                    "items": [
                        {
                            "mime": "application/vnd.code.notebook.stdout",
                            "value": [
                                "true",
                                "false",
                                "true",
                                ""
                            ]
                        }
                    ]
                }
            ]
        },
        {
            "language": "markdown",
            "source": [
                "## 转译  \n新语法转换为等价旧版本的语法。有些新语法无法转换为旧语法表示。\n新语法更容易阅读和维护。"
            ],
            "outputs": []
        },
        {
            "language": "markdown",
            "source": [
                "## 宿主对象  \n由运行环境提供的，而非JS规范定义。  \n- window\n- document"
            ],
            "outputs": []
        }
    ]
}