Question

在@types/d3定义中，各行如下：

export type ValueFn<T extends BaseType, Datum, Result> = (this: T, datum: Datum, index: number, groups: T[] | ArrayLike<T>) => Result;

attrTween(name: string): ValueFn<GElement, Datum, (t: number) => string> | undefined;

当我使用函数attrTween时，我会像这样使用它：

caller.attrTween("points", (d, index, groups) => { return (t) => {return "";};  }

呼叫者为Transition<BaseType, PieArcDatum<number>

这些参数由VSCode推断为：

(parameter) d: d3.PieArcDatum<number>
(parameter) index: number
(parameter) groups: d3.BaseType[] | d3.ArrayLike<d3.BaseType>

类型定义如何强制执行此行为？可以逐字解释，特别是通用用法吗？

Answer 1

attrTween具有three separate overloads，其中第三个条目（只有带有非空第二个参数的两个参数重载）是：

/**
 * Assign the attribute tween for the attribute with the specified name to the specified interpolator factory.
 * An interpolator factory is a function that returns an interpolator; when the transition starts, the factory is evaluated for each selected element.
 * The returned interpolator will then be invoked for each frame of the transition, in order,
 * being passed the eased time t, typically in the range [0, 1]. Lastly, the return value of the interpolator will be used to set the attribute value.
 * The interpolator must return a string.
 *
 * @param name Name of attribute.
 * @param factory An interpolator factory which is evaluated for each selected element, in order, being passed the current datum (d),
 * the current index (i), and the current group (nodes), with this as the current DOM element (nodes[i]). The interpolator factory returns a string interpolator,
 * which takes as its argument eased time t, typically in the range [0, 1] and returns the interpolated string.
 */
attrTween(name: string, factory: ValueFn<GElement, Datum, (t: number) => string>): this;

与您列出的过载相比，它与您的呼叫的匹配要好得多。此定义存在于“过渡”中，定义如下：

export interface Transition<GElement extends BaseType, Datum, PElement extends BaseType, PDatum>

有了这个，我们可以看到直接映射：

d是Datum，而caller中的d3.PieArcDatum<number>
index是number
groups是T[] | ArrayLike<T>，其中T extends BaseType。
- 根据attrTween的定义，T中的ValueFn与GElement中的Transition相同。
- GElement是BaseType中的callee。
- 因此，T是BaseType，所以groups是d3.BaseType[] | d3.ArrayLike<d3.BaseType>。

了解打字稿定义

1 个答案: