重构代码时无法读取未定义的属性"push" [英] Cannot read property 'push' of undefined when refactoring code
问题描述
我想使这段代码更简单:
I want to make this code easier:
links.forEach(function(link) {
link.source = nodes[link.source] ||
(nodes[link.source] = {
name: link.source
});
link.target = nodes[link.target] ||
(nodes[link.target] = {
name: link.target
});
console.log(nodes)
});
所以，我像这样重构它:
So, I refactored it like this:
links.forEach(function(link) {
if (nodes[link.source] == null) {
nodes[link.source] = {
name: link.source
};
} else if (nodes[link.target] == null) {
nodes[link.target] = {
name: link.target
};
} else {
console.log('Not problem');
}
});
但是，现在出现此错误:
However, now I get this error:
无法读取未定义的属性"push"
Cannot read property 'push' of undefined
这是完整的原始代码:
<DOCTYPE html>
<meta charset="utf-8">
<style>
.node {
fill: #4D00DD;
stroke: #fff;
stroke-width: 2px;
}
.link {
stroke: #777;
stroke-width: 8px;
}
</style>
<body>
<script src="https://d3js.org/d3.v3.min.js"></script>
<script>
var width = 1080,
height = 960;
var links = [
{ source : "Baratheon", target : "Lannister"},
{ source : "Baratheon", target : "Stark"},
{ source : "Lannister", target : "Stark"},
];
var nodes = {};
// parse links to nodes
links.forEach(function(link) {
link.source = nodes[link.source] ||
(nodes[link.source] = {name: link.source});
link.target = nodes[link.target] ||
(nodes[link.target] = {name: link.target});
console.log(nodes)
});
// add svg to our body
var svg = d3.select("body").append("svg")
.attr("width", width)
.attr("height", height);
var force = d3.layout.force()
.size([width, height])
.nodes(d3.values(nodes))
.links(links)
.on("tick", tick)
.linkDistance(600)
.start();
var link = svg.selectAll(".link")
.data(links)
.enter().append("line")
.attr("class", "link")
var node = svg.selectAll(".node")
.data(force.nodes())
.enter().append("circle")
.attr("class", "node")
.attr("r", width * 0.03);
function tick(e) {
node.attr("cx", function(d) { return d.x; })
.attr("cy", function(d) { return d.y; })
.call(force.drag);
link.attr("x1", function(d) { return d.source.x; })
.attr('y1', function(d) { return d.source.y; })
.attr('x2', function(d) { return d.target.x; })
.attr("y2", function(d) { return d.target.y; })
}
</script>
推荐答案
您试图使该块更易于阅读，这是一个非常不错的练习.但是，您忘记了一些东西.
You tried to make that block easier to read, which is a very nice exercise. However, you forgot something.
在原始代码中，此任务...
In the original code, this assignment...
link.source = nodes[link.source] || (nodes[link.source] = {name: link.source});
...意味着，非常冗长:
... means, in a very verbose way:
nodes[link.source]是否存在?如果是，请创建link.source = nodes[link.source].如果否，请先创建nodes[link.source] = {name: link.source}，然后再创建link.source = nodes[link.source].
Does
nodes[link.source]exist? If yes, makelink.source = nodes[link.source]. If no, makenodes[link.source] = {name: link.source}, and then makelink.source = nodes[link.source].
但是在您的if逻辑中，如果nodes[link.source]存在，就永远不会设置link.source！
But in your if logic you're never setting link.source if nodes[link.source] exists!
此外，您不需要:
if (nodes[link.source] == null) {
一个简单的if (!nodes[link.source]) {即可使用.
最后，放下else.无论第一个if的结果如何，都必须对第二个if 进行评估.
Finally, drop that else. The second if must be evaluated, regardless the result of the first if.
话虽如此，这应该是您的重构代码:
All that being said, this should be your refactored code:
links.forEach(function(link) {
if (!nodes[link.source]) {
nodes[link.source] = {
name: link.source
}
};
//Look, Ma, no 'else' here!
if (!nodes[link.target]) {
nodes[link.target] = {
name: link.target
}
};
//add these lines:
link.source = nodes[link.source];
link.target = nodes[link.target];
});
这是正在运行的演示:
var width = 600,
height = 300;
var links = [{
source: "Baratheon",
target: "Lannister"
}, {
source: "Baratheon",
target: "Stark"
}, {
source: "Lannister",
target: "Stark"
},
];
var nodes = {};
links.forEach(function(link) {
if (!nodes[link.source]) {
nodes[link.source] = {
name: link.source
}
};
if (!nodes[link.target]) {
nodes[link.target] = {
name: link.target
}
};
link.source = nodes[link.source];
link.target = nodes[link.target];
});
// add svg to our body
var svg = d3.select("body").append("svg")
.attr("width", width)
.attr("height", height);
var force = d3.layout.force()
.size([width, height])
.nodes(d3.values(nodes))
.links(links)
.on("tick", tick)
.linkDistance(50)
.start();
var link = svg.selectAll(".link")
.data(links)
.enter().append("line")
.attr("class", "link")
var node = svg.selectAll(".node")
.data(force.nodes())
.enter().append("circle")
.attr("class", "node")
.attr("r", width * 0.03);
function tick(e) {
node.attr("cx", function(d) {
return d.x;
})
.attr("cy", function(d) {
return d.y;
})
.call(force.drag);
link.attr("x1", function(d) {
return d.source.x;
})
.attr('y1', function(d) {
return d.source.y;
})
.attr('x2', function(d) {
return d.target.x;
})
.attr("y2", function(d) {
return d.target.y;
})
}
<script src="https://d3js.org/d3.v3.min.js"></script>
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