如何检查儿童功能是否存在（聚合物）

Question

父

check() {
  if(typeof this.$.child.function() == 'function') {
    // do something
  }
}

如何检查子功能是否存在？

抛出

  

Uncaught TypeError：this。$。child.function不是函数

Answer 1

Probably the main problem with your code is that you are actually calling the function with the parenthesis () and then comparing the result with the string 'function'. To check the existence remove the parenthesis:

if (this.$.child.function == 'function') { /* ... */ };

However the error could also be caused by this.$.child being undefined when called. This can happen if you're trying to access your component's static node map (this.$) when Polymer hasn't initialised it yet.

The map is accessible in the ready lifecycle callback: see here.

Answer 2

Assuming you are not using the reserved keyword 'function' as a method name the following should work perfectly fine:

check() {
  if(typeof this.$.child.someFunDefinedInChild == 'function') {
  //do work
  }
}