= > pull-down bottoming event on the page
= > handle waterfall stream effect function (image preload function callback is required to perform picture output)
= > picture preload function
now I don"t know how to determine the completion of loading and adding callback
in the picture preload function , because in WeChat Mini Programs, the picture loading is completed with bindload event
of the Image component bindload event
if there are 5 pictures, how to add the callback after loading 5 pictures in the callback of bindload event Synchronize to picture preload function so that it can judge and add callback?