如何理解Vue的render函数

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洪定伦
    阅读 13 分钟
    137

    第一个参数(必须) - {String | Object | Function}

    <!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>render</title>
    <script src="https://cdn.bootcss.com/vue/2.3.4/vue.js"></script>
</head>
<body>
    <div id="app">
        <elem></elem>
    </div>
    <script>
        Vue.component('elem', {
            render: function(createElement) {
                return createElement('div');//一个HTML标签字符
                /*return createElement({
                    template: '<div></div>'//组件选项对象
                });*/
                /*var func = function() {
                    return {template: '<div></div>'}
                };
                return createElement(func());//一个返回HTML标签字符或组件选项对象的函数*/
            }
        });
        new Vue({
            el: '#app'
        });
    </script>
</body>
</html>

    第二个参数(可选) - {Object}

    <!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>render</title>
    <script src="https://cdn.bootcss.com/vue/2.3.4/vue.js"></script>
</head>
<body>
    <div id="app">
        <elem></elem>
    </div>
    <script>
        Vue.component('elem', {
            render: function(createElement) {
                var self = this;
                return createElement('div', {//一个包含模板相关属性的数据对象
                    'class': {
                        foo: true,
                        bar: false
                    },
                    style: {
                        color: 'red',
                        fontSize: '14px'
                    },
                    attrs: {
                        id: 'foo'
                    },
                    domProps: {
                        innerHTML: 'baz'
                    }
                });
            }
        });
        new Vue({
            el: '#app'
        });
    </script>
</body>
</html>

    第三个参数(可选) - {String | Array}

    <!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>render</title>
    <script src="https://cdn.bootcss.com/vue/2.3.4/vue.js"></script>
</head>
<body>
    <div id="app">
        <elem></elem>
    </div>
    <script>
        Vue.component('elem', {
            render: function(createElement) {
                var self = this;
                // return createElement('div', '文本');//使用字符串生成文本节点
                return createElement('div', [//由createElement函数构建而成的数组
                    createElement('h1', '主标'),//createElement函数返回VNode对象
                    createElement('h2', '副标')
                ]);
            }
        });
        new Vue({
            el: '#app'
        });
    </script>
</body>
</html>

    两种组件写法对比

    <!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>render</title>
    <script src="https://cdn.bootcss.com/vue/2.3.4/vue.js"></script>
</head>
<body>
    <div id="app">
        <ele></ele>
    </div>
    <script>
        /*Vue.component('ele', {
            template: '<div id="elem" :class="{show: show}" @click="handleClick">文本</div>',
            data: function() {
                return {
                    show: true
                }
            },
            methods: {
                handleClick: function() {
                    console.log('clicked!');
                }
            }
        });*/
        Vue.component('ele', {
            render: function(createElement) {
                return createElement('div', {
                    'class': {
                        show: this.show
                    },
                    attrs: {
                        id: 'elem'
                    },
                    on: {
                        click: this.handleClick
                    }
                }, '文本');
            },
            data: function() {
                return {
                    show: true
                }
            },
            methods: {
                handleClick: function() {
                    console.log('clicked!');
                }
            }
        });
        new Vue({
            el: '#app'
        });
    </script>
</body>
</html>

    this.$slots用法

    <!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>render</title>
    <script src="https://cdn.bootcss.com/vue/2.3.4/vue.js"></script>
</head>
<body>
    <div id="app">
        <blog-post>
            <h1 slot="header"><span>About Me</span></h1>
            <p>Here's some page content</p>
            <p slot="footer">Copyright 2016 Evan You</p>
            <p>If I have some content down here</p>
        </blog-post>
    </div>
    <script>
        Vue.component('blog-post', {
            render: function(createElement) {
                var header = this.$slots.header,//返回由VNode组成的数组
                    body = this.$slots.default,
                    footer = this.$slots.footer;
                return createElement('div', [
                    createElement('header', header),
                    createElement('main', body),
                    createElement('footer', footer)
                ])
            }
        });
        new Vue({
            el: '#app'
        });
    </script>
</body>
</html>

    使用props传递数据

    <!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>render</title>
    <script src="https://cdn.bootcss.com/vue/2.3.4/vue.js"></script>
</head>
<body>
    <div id="app">
        <ele :show="show"></ele>
        <ele :show="!show"></ele>
    </div>
    <script>
        Vue.component('ele', {
            render: function(createElement) {
                if (this.show) {
                    return createElement('p', 'true');
                } else {
                    return createElement('p', 'false');
                }
            },
            props: {
                show: {
                    type: Boolean,
                    default: false
                }
            }
        });
        new Vue({
            el: '#app',
            data: {
                show: false
            }
        });
    </script>
</body>
</html>

    VNodes必须唯一

    <!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>render</title>
    <script src="https://cdn.bootcss.com/vue/2.3.4/vue.js"></script>
</head>
<body>
    <!-- VNode必须唯一 -->
    <div id="app">
        <ele></ele>
    </div>
    <script>
        var child = {
            render: function(createElement) {
                return createElement('p', 'text');
            }
        };
        /*Vue.component('ele', {
            render: function(createElement) {
                var childNode = createElement(child);
                return createElement('div', [
                    childNode, childNode//VNodes必须唯一，渲染失败
                ]);
            }
        });*/
        Vue.component('ele', {
            render: function(createElement) {
                return createElement('div', 
                    Array.apply(null, {
                        length: 2
                    }).map(function() {
                        return createElement(child)//正确写法
                    })
                );
            }
        });
        new Vue({
            el: '#app'
        })
    </script>
</body>
</html>

    v-model指令

    <!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>render</title>
    <script src="https://cdn.bootcss.com/vue/2.3.4/vue.js"></script>
</head>
<body>
    <div id="app">
        <el-input :name="name" @input="val=>name=val"></el-input>
        <div>你的名字是{{name}}</div>
    </div>
    <script>
        Vue.component('el-input', {
            render: function(createElement) {
                var self = this;
                return createElement('input', {
                    domProps: {
                        value: self.name
                    },
                    on: {
                        input: function(event) {
                            self.$emit('input', event.target.value);
                        }
                    }
                })
            },
            props: {
                name: String
            }
        });
        new Vue({
            el: '#app',
            data: {
                name: 'hdl'
            }
        });
    </script>
</body>
</html>

    作用域插槽

    <!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>render</title>
    <script src="https://cdn.bootcss.com/vue/2.3.4/vue.js"></script>
</head>
<body>
    <div id="app">
        <ele>
            <template scope="props">
                <span>{{props.text}}</span>
            </template>
        </ele>
    </div>
    <script>
        Vue.component('ele', {
            render: function(createElement) {
                // 相当于<div><slot :text="msg"></slot></div>
                return createElement('div', [
                    this.$scopedSlots.default({
                        text: this.msg
                    })
                ]);
            },
            data: function() {
                return {
                    msg: '来自子组件'
                }
            }
        });
        new Vue({
            el: '#app'
        });
    </script>
</body>
</html>

    向子组件中传递作用域插槽

    <!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>render</title>
    <script src="https://cdn.bootcss.com/vue/2.3.4/vue.js"></script>
</head>
<body>
    <div id="app">
        <ele></ele>
    </div>
    <script>
        Vue.component('ele', {
            render: function(createElement) {
                return createElement('div', [
                    createElement('child', {
                        scopedSlots: {
                            default: function(props) {
                                return [
                                    createElement('span', '来自父组件'),
                                    createElement('span', props.text)
                                ];
                            }
                        }
                    })
                ]);
            }
        });
        Vue.component('child', {
            render: function(createElement) {
                return createElement('b', this.$scopedSlots.default({text: '我是组件'}));
            }
        });
        new Vue({
            el: '#app'
        });
    </script>
</body>
</html>

    函数化组件

    <!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>render</title>
    <script src="https://cdn.bootcss.com/vue/2.3.4/vue.js"></script>
</head>
<body>
    <div id="app">
        <smart-item :data="data"></smart-item>
        <button @click="change('img')">切换为图片为组件</button>
        <button @click="change('video')">切换为视频为组件</button>
        <button @click="change('text')">切换为文本组件</button>
    </div>
    <script>
        // 图片组件选项
        var ImgItem = {
            props: ['data'],
            render: function(createElement) {
                return createElement('div', [
                    createElement('p', '图片组件'),
                    createElement('img', {
                        attrs: {
                            src: this.data.url
                        }
                    })
                ]);
            }
        }
        // 视频组件
        var VideoItem = {
            props: ['data'],
            render: function(createElement) {
                return createElement('div', [
                    createElement('p', '视频组件'),
                    createElement('video', {
                        attrs: {
                            src: this.data.url,
                            controls: 'controls',
                            autoplay: 'autoplay'
                        }
                    })
                ]);
            }
        };
        /*纯文本组件*/
        var TextItem = {
            props: ['data'],
            render: function(createElement) {
                return createElement('div', [
                    createElement('p', '纯文本组件'),
                    createElement('p', this.data.text)
                ]);
            }
        };

        Vue.component('smart-item', {
            functional: true,
            render: function(createElement, context) {
                function getComponent() {
                    var data = context.props.data;
                    if (data.type === 'img') return ImgItem;
                    if (data.type === 'video') return VideoItem;
                    return TextItem;
                }
                return createElement(
                    getComponent(),
                    {
                        props: {
                            data: context.props.data
                        }
                    },
                    context.children
                )
            },
            props: {
                data: {
                    type: Object,
                    required: true
                }
            }
        });
        new Vue({
            el: '#app',
            data() {
                return {
                    data: {}
                }
            },
            methods: {
                change: function(type) {
                     if (type === 'img') {
                        this.data = {
                            type: 'img',
                            url: 'https://raw.githubusercontent.com/iview/iview/master/assets/logo.png'
                        }
                    } else if (type === 'video') {
                        this.data = {
                            type: 'video',
                            url: 'http://vjs.zencdn.net/v/oceans.mp4'
                        }
                    } else if (type === 'text') {
                        this.data = {
                            type: 'text',
                            content: '这是一段纯文本'
                        }
                    }
                }
            },
            created: function() {
                this.change('img');
            }
        });
    </script>
</body>
</html>
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