Typescript assignment causes compilation error

Question

Typescript is giving me a compilation error with the following code:

console.log('YHISTORY:login: data = '+data);
let theData = JSON.parse(data);
console.log('YHISTORY:login: theData = '+JSON.stringify(theData));

It complains when compiling the second line as follows:

Error TS2345: Argument of type '{}' is not assignable to parameter of type 'string'

When I run this code the first line generates this console output:

YHISTORY:login: data = {"key":"4ba9f2eec3a59e76799a728f0dcda831b7f1fb66"}

The third line does not produce any console output. The following error is generated:

EXCEPTION: Error: Uncaught (in promise): TypeError: this is null

SergeyK · Accepted Answer · 2016-08-23 12:38:33Z

1

The error is not about assignment, it's about calling JSON.parse() function. Error looks like your data variable is already an object, when string is expected as function argument.

You can reproduce this error with this example:

var data = {};
JSON.parse(data);

answered Aug 23, 2016 at 12:38

SergeyK

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3 Comments

Bill Noble Over a year ago

The typeof data is string.

SergeyK Over a year ago

Then there is not enough information for suggestion. In theory Error TS2345 can be incorrect while using incorrect .d.ts typescript definitions. It can be declared as object, but javascript still returns string. What about exception it looks like not aligned to this lines of code. I can suggest some scoping problems somewhere inside Promise handling, as an example using function(){} notation without binding this.

Bill Noble Over a year ago

The problem tuned out to be using .then(function(data) { rather than .then((data:any)=>{ in the promise handler

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