“TypeError”：无法读取 Vuejs 中未定义的属性？

Question

It works like this: I have a table made in Vue, where I have some select options. This error appears when I have a grupo (group) and this group is not associated with a maquina (machine), what shouldn't happen, the objective is that only "-" appears. Throws an error in the console and does not show in my DataTable.

The error: [/Vue warn]: Error in render: "TypeError: Cannot read properties of undefined (reading 'id_area')

This is the part of my code that I believe is causing this error:

computed: {
    linhas () {
        return this.lista.map(row => {
            const group = this.grupos.find(g => g.id === row.id_grupo);
            const machine = this.maquinas.find(m => m.id === group.id_maquina);
            const area = this.areas.find(a => a.id === machine.id_area);

            return ({
                href: {path: this.editRoute + row.id},
                cols: [
                    row.id,
                    row.tag,
                    row.descricao,
                    row.tipo === "ANALOGICA" ? "Analógica" : "Digital",
                    group.nome,
                    (machine || { nome: "-" }).nome,
                    (area || { nome: "-" }).nome
                ]
            });
        });
    }
},

Can someone help me? I do not understand why this happening.

Answer 1

The array.find() method returns undefined if the value is not found ( https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/find ).

So if ther is no "machina" with the id group.id_maquina retrieve from the previous line, the line const machine = this.maquinas.find(m => m.id === group.id_maquina); set value undefined to the machine const.

And here's your error happens: reading id_area from machine that is undefined.

So you have to check if your variables are not undefined after array.find()

//...
  const group = this.grupos.find(g => g.id === row.id_grupo);
  if (group) {
    const machine = this.maquinas.find(m => m.id === group.id_maquina);
    if (machine) {
      const area = this.areas.find(a => a.id === machine.id_area);
    }
  }
//...