未捕获的TypeError：jQuery（...）。css（...）。mCustomScrollbar不是函数

Question

Code

Javascript Error in console

这是代码。

---------- ##代码##

function Init_BodyConv() {
jQuery(".um-profile-body.messages .um-message-autoheight").css({
    "max-height": "500px"
}).mCustomScrollbar({
    theme: "dark-3",
    mouseWheelPixels: 500
}).mCustomScrollbar("scrollTo", "bottom", {
    scrollInertia: 0
}),
jQuery(".um-message-conv").length && jQuery(".um-message-conv").css({
    "max-height": "500px"
}).mCustomScrollbar({
    theme: "dark-3",
    mouseWheelPixels: 500
})

}