How to use the object-assign.default function in object-assign

function updatedErrorState(initialState:IApplicationState, error:string, resetValue:string):IApplicationState{
	const errors = (initialState.errors ? addError(initialState.errors, error) : [error]);
	return objectAssign({}, initialState, {errors, [resetValue]:0});
}

function changeColor(initialState:IApplicationState, color:string){
	return objectAssign({}, initialState, {"color":color});
}

function changeWidth(initialState:IApplicationState, width:any):IApplicationState {
	if(isValidNumeric(width)){
		return updatedErrorState(initialState, widthError, "width");
	}
	
	const errors = removeError(initialState.errors, widthError);
	return objectAssign({}, initialState, {width,errors});
}

function changeHeight(initialState:IApplicationState, height:any):IApplicationState {
	if(isValidNumeric(height)){
		return updatedErrorState(initialState, heightError, "height");
	}
	
	const errors = removeError(initialState.errors, heightError);	
	return objectAssign({}, initialState, {height, errors});
}