guard function that returns if val is truthy
守卫函数，返回 val 是否为真值
The type of elements in the array / 数组元素的类型
The value to check. 要检查的值
True if the value is truthy, false otherwise. 如果值为真值则返回true，否则返回false
[1, 2, 3, '', false, undefined].filter(toTruthy) // => [1, 2, 3] Copy
[1, 2, 3, '', false, undefined].filter(toTruthy) // => [1, 2, 3]
guard function that returns if val is truthy
守卫函数，返回 val 是否为真值