html部分：

                <div class="help ml20" @click="fullScreen">
                    <i class="el-icon-full-screen sideBar-el-icon"></i>
                </div>

js部分(isFllScreen是判斷是否開了全屏用的變數)：

        fullScreen() {
            let docElm = document.documentElement;
            
 
if (this.isFllScreen) {
                if (document.exitFullscreen) {
                    document.exitFullscreen();
                }
                else if (document.mozCancelFullScreen) {
                    document.mozCancelFullScreen();
                }
                else if (document.webkitCancelFullScreen) {
                    document.webkitCancelFullScreen();
                }
                
 
else if (document.msExitFullscreen) {
                    document.msExitFullscreen();
                }
                this.isFllScreen = false
            } else {
                //W3C   
                if (docElm.requestFullscreen) {
                    docElm.requestFullscreen();
                }
                
 
//FireFox   
                else if (docElm.mozRequestFullScreen) {
                    docElm.mozRequestFullScreen();
                }
                //Chrome等   
                else if (docElm.webkitRequestFullScreen) {
                    docElm.webkitRequestFullScreen();
                }
                this.isFllScreen = true
            }
        }

效果：