代码之家 › 专栏 › 技术社区 › Milenko Markovic

如何使用非空断言重构我的代码?对象可能“未定义”

typescript

Milenko Markovic · 技术社区 · 6 月前

我有问题

export const tfModules = (moduleIds: readonly string[], mapping: Map<string, [string, string]>): string[] =>
  moduleIds.map(m => mapping.get(m).at(0))
    .filter(m => m !== undefined)
    .map(m => m!);

得到了

error TS2532: Object is possibly 'undefined'.

使用非null断言来告诉值不能为null或undefined的最简单方法是什么?

1 回复 | 直到 6 月前

Alexander Nenashev 6 月前

你可以 mapping.get(m)! :

export const tfModules = (moduleIds: readonly string[], mapping: Map<string, [string, string]>): string[] =>
  moduleIds.map(m => mapping.get(m)!.at(0)).filter(m => m !== undefined)

Playground

一个没有非空断言的更快版本:

export const tfModules = (moduleIds: readonly string[], mapping: Map<string, [string, string]>): string[] =>
  moduleIds.reduce((r, m) => {
    const found = mapping.get(m);
    found && r.push(found[0]);
    return r;
  }, [] as string[]);