需要帮助->未捕获（承诺）TypeError：无法读取未定义的属性“ length”

Question

I have a website and when I am trying to create new content and choose a category I have an error. Did you happend to have this issue before?

I dont know to resolve this.

     setHierarchyPaths: function (categories, path) {
        for (var i = 0; i < categories.length; i++) {
            if (typeof path !== 'undefined') {
                categories[i].path = path + '.' + categories[i].id;
            } else {
                categories[i].path = categories[i].id;
            }

            if (categories[i].childrens.length > 0) {
                this.setHierarchyPaths(categories[i].childrens, 
      categories[i].path);
            }

            // We need a flat tree!
            this.flatTree.push(categories[i]);
        }
    },

I have uploaded the error on these 2 pictures. Hope you can help me with this. https://www.screencast.com/t/PWjbxIgJe

https://www.screencast.com/t/Jt2RN08G

Many thanks

Answer 1

This is a quite common kind of error. It happens when you try to access the attribute (or method) of an object that does not exist.

An example

const myObject: SomeObject;
if ( myObject.length === 0) {... }

In this case myObjec is declared but still undefined.
So, as a result, the length attribute is called on undefined. And you will get the error "cannot read property length of undefined".

In your case, please check how the method setHierarchyPaths is called, because it seems (as jonrsharpe already said in the comment), that the parameter categories was provided with an undefined value.