d3.json回调函数 [英] d3.json callback function

问题描述

我正在使用d3.js 3.4.13，文档说d3.json(data, callback)的回调函数应采用callback(error, responseData)格式，但是，我发现它实际上将数据设置为第一个参数，并且第二个参数是不必要的，所以我改用callback(responseData).它可以工作，但是我很困惑为什么它不能以我解释文档来描述它的方式来工作.我想念什么?

I'm using d3.js 3.4.13, and the docs say the callback function for d3.json(data, callback) should be of the format callback(error, responseData), however, I found that it actually sets the data to the first parameter, and the second parameter is unnecessary, so I use callback(responseData) instead. It works, but I'm confused why it doesn't work the same way I interpreted the docs to describe it. What am I missing?

推荐答案

快速浏览源揭示了以下功能:

A quick look at the source reveals the following function:

function d3_xhr_fixCallback(callback) {
  return callback.length === 1
      ? function(error, request) { callback(error == null ? request : null); }
      : callback;
}

D3通过.length显式检查回调参数，如果只有一个，则将数据放入其中.

D3 explicitly checks the number of arguments to the callback through .length and if there's only one, puts the data in it.

因此，一个参数的版本是仍然可以按预期工作的便捷版本.

So the one-argument version is a convenience version that still works as expected.

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