[英]How to declare that a var has now been initialized, if Flow can't infer it automatically?
Try this code in Flow's REPL : 在Flow的REPL中尝试以下代码 :
const numbers = [5, 3, 22, 2, 6];
let max: number;
numbers.forEach(item => {
if (!max || item > max) max = item;
});
console.log(max++); // type error
I can be certain that max
will have been initialized as a number before the max++
expression. 我可以确定max
将被初始化为max++
表达式之前的数字。 But Flow can't infer this automatically, so it complains. 但是Flow无法自动推断出这一点,因此它会抱怨。
I want to say to Flow, after the forEach: please assume the max
variable has now been initialized. 我要对Flow说,在forEach之后:请假设max
变量现在已经初始化。 Is there a way to do this? 有没有办法做到这一点?
(Related – Flow has 'declarations': declare var max: number;
– this lets you declare that a number variable called var
exists in global scope. But you can't use it to redeclare something already declared in your own scope.) (相关– Flow具有“声明”: declare var max: number;
–这使您可以声明全局范围内存在一个名为var
的数字变量。但是您不能使用它来重新声明已经在自己的范围内声明的内容。)
You can initialize max by let max: number = numbers[0];
您可以通过let max: number = numbers[0];
初始化max let max: number = numbers[0];
. 。 That should stop flow from complaining. 那应该阻止人们抱怨。
You can also rewrite your code in a less mutable way: 您还可以用一种不太易变的方式重写代码:
const numbers = [5, 3, 22, 2, 6];
const max = numbers.reduce((max, item) => item > max ? item : max,
Number.NEGATIVE_INFINITY);
console.log(max + 1);
This avoids any kind of mutation, making the life easier for Flow (and probably for humans too :) ) 这样可以避免任何形式的变异,从而使Flow的生活更加轻松(也可能对人类来说也很容易:))
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