Some type declarations are wrong.

[sgkim126]

• The parameter of AssetMintOutput.fromJSON is not declared as JSON object.
  

  codechain-sdk-js/src/core/transaction/AssetMintOutput.ts

  Lines 13 to 16 in 023fb7e

  	public static fromJSON(data: {
  	lockScriptHash: string;
  	parameters: Buffer[];
  	amount: number | null;

• The parameter of AssetTransferOutput.fromJSON is not declared as JSON object.
  

  codechain-sdk-js/src/core/transaction/AssetTransferOutput.ts

  Line 33 in 023fb7e

  public static fromJSON(data: AssetTransferOutputData) {

• output field of the parameter of AssetMintTransaction should not be a AssetMintOutput
  

  codechain-sdk-js/src/core/transaction/AssetMintTransaction.ts

  Lines 67 to 82 in 023fb7e

  	constructor(data: {
  	networkId: NetworkId;
  	shardId: number;
  	metadata: string;
  	output: AssetMintOutput;
  	registrar: PlatformAddress | null;
  	nonce: number;
  	}) {
  	const { networkId, shardId, metadata, output, registrar, nonce } = data;
  	this.networkId = networkId;
  	this.shardId = shardId;
  	this.metadata = metadata;
  	this.output = new AssetMintOutput(output);
  	this.registrar = registrar;
  	this.nonce = nonce;
  	}

[joojis]

Fixed at: #253

Regarding the third item, I changed the constructor implementation instead of changing the type.
(e9e7bd5#diff-f2ab1e482bebb9418aec037539b0b051L82)