Motoko <>Typescript : Array

Developers
1

Hello community, I’m facing a misunderstanding with arrays from Motoko and Typescript.

Here is the problem:

// Motoko file
public type Entity = {
	tagList: ?[Text];
};

// Generated Typescript file
export interface Entity {
	'tagList': [] | [Array<string>]
};

And now the problems I’m facing in my Typescript frontend file :

/**
 *  IDE Error :
 *  Type 'string[]' is not assignable to type '[] | [string[]]'.
 */
public buildEntity(tagList: string[]): void {
	const entity: Entity = {
		tagList: tagList
	};
};

/**
 *  Not used, just to test
 *  IDE Error :
 *  Type '{ tagList: [string[]]; }' is missing the following properties from type 'Entity'
 */
public buildEntity(tagList: [string[]]): void {
	const entity: Entity = {
		tagList: tagList
	};
};

/**
 *  Runtime Error :
 *  Invalid opt record {tagList:opt vec text;} argument: [{"tagList":["tag1","tag2"]}]
 */
public buildEntity(tagList: []): void {
	const entity: Entity = {
		tagList: tagList
	};
};

Coming from Java, I am used to strong typing and I wonder if the problem does not come from there… Or maybe I missed something that is right in front of my eyes.

Could someone give me some help on this problem?

2

The js agent uses arrays to handle opt values. if you have an opt array you need to look for an array in an array.

would be null
[] would be an empty array
[[val,val]] would be an array with data in it

1 Like
3

Ok I solved the problem by removing the optional syntax from the Motoko tagList field.

// Motoko file
public type Entity = {
	tagList: [Text];
};

// Generatered Typescript file
export interface Entity {
    'tagList' : Array<string>,
};

In the end, it seems more relevant to have an empty Array rather than a null one.