类型错误：无法使用 AngularJS 读取未定义的属性“推送”

Question

I'm trying to push my data into this CompareArray but get the following error:

TypeError: Cannot read property 'push' of undefined
    at Object.addResult (src\services\CompareService.js:22)

Code:

this.addResult = function (type, result) {
    this[type.toLowerCase() + 'CompareArray'].push(result);
    this.checkToDisplayLinks(type);
    this.checkToDisableCheckboxes(type);
};

Answer 1

Before you push anything check if it is undefined and initialized

if(this[type.toLowerCase() + 'CompareArray']){
 this[type.toLowerCase() +  'CompareArray'].push(result);
}
else
{
   this[type.toLowerCase() +  'CompareArray'] = [result];
}

Answer 2

if you look closely, error is self descriptive.

Cannot read property 'push' of undefined at Object.addResult 

addResult is your method. You are doing "push" on

this[type.toLowerCase() + 'CompareArray'].push(result);

for which it says - 'push' of undefined. which means

this[type.toLowerCase() + 'CompareArray'] 

is undefined. Push is a method only available on arrays.

Hope this helps.