TypeError - 无法将未定义或 null 转换为 object。 尝试将 state object 值转换为 json 数组字符串

Question

While trying to fit the input form data to a JSON array string, I am getting an error

Cannot convert undefined or null to object.

Below is the code which I tried to use on the state data:

const test = this.state.values;
Object.keys(test).forEach(key=>test[key]=[test[key]]);

When I do console.log(test) the data is as below:

Object
input1: {i: "ytuy"}
input2: {x: "tyutyu"}

My final goal is to have the JSON output as:

{
   "input1":[{"i":"ytuy"}],
   "input2":[{"x":"tyutyu"}]
}

Can anyone suggest why I get this error?

Answer 1

It looks like what you are trying to do is to to each property value into a single-entry array. You can do that by mapping your object with Object.fromEntries and Object.entries .

As mentioned in the comments, it is critical that you do not mutate the current object since this will mutate your component's state.

 const test = { input1: {i: "ytuy"}, input2: {x: "tyutyu"} } const mapped = Object.fromEntries( Object.entries(test).map( ([key, value]) => [key, [value]] ) ); console.log(JSON.stringify(mapped));

That will print out

{"input1":[{"i":"ytuy"}],"input2":[{"x":"tyutyu"}]}

The particular error that you got sounds like perhaps this.state.values is sometimes null or undefined and it not always an object . So you'll want to make sure that the object exists before trying to map it.

Answer 2

since mutating the state object is not allowed in react js, here is the fix for my issue.

let obj = Object.assign({}, test );  // creates a brand new object
Object.keys(obj).forEach(key=>obj[key]=[obj[key]]);