我正在用JavaScript构造一个生成器,我不确定构建器通常如何处理可选的未定义值。我想如果字段未定义,生成器不会将可选字段附加到对象。这对建筑商来说是可以接受的吗?如果没有,还有什么替代方案?
下面是构建器不附加未定义的可选的第一个实现的示例:
建筑工人:
function Thing(required1, required2, required3) {
//check required params
var fields = {
required1: required1,
required2: required2,
required3: required3
};
var _withOptionalParam = function(param) {
if(!param) { return this; } //exit function early if param is undefined
fields.param = param;
return this;
};
var _build = function() {
var result = fields;
return result;
};
var builder = {
withOptionalParam: _withOptionalParam,
build: _build
};
return builder;
}
在行动中:
var thing = new Thing("foo","bar","baz").withOptionalParam(undefined).build();
//'thing' should be
// {
// required1:"foo",
// required2:"bar",
// required3:"baz"
// };
//
提前感谢!
我认为您在_withOptinalParam
函数中丢失了this
的上下文。你可以bind
fields
反对它作为this
上下文。
function Thing(required1, required2, required3) {
//check required params
var fields = {
required1: required1,
required2: required2,
required3: required3
};
var _withOptionalParam = function(param) {
if(!param) { return this; } //exit function early if param is undefined
fields.param = param;
return this;
};
var _build = function() {
var result = fields;
return result;
};
var builder = {
withOptionalParam: _withOptionalParam.bind(fields),
build: _build
};
return builder;
}
var thing = new Thing("foo","bar","baz").withOptionalParam(undefined);
console.log( thing );
//'thing' should be
// {
// required1:"foo",
// required2:"bar",
// required3:"baz"
// };
//
<script src="http://codepen.io/synthet1c/pen/WrQapG.js"></script>