将任务更改为函数后，只需使用即可；

After changing your tasks to functions, simply use;

gulp.task('default', gulp.series (watch, gulp.parallel(styles, scripts, images),

    function (done) { done(); }    
));

首先运行watch函数，然后并行运行样式，脚本和图像函数.

The watch function will run first, then the styles, scripts and images functions in parallel.

从 gulp.series文档:

组合物的嵌套深度没有强加限制 使用series()和parallel()进行操作.

There are no imposed limits on the nesting depth of composed operations using series() and parallel().