定义函数类型

函数类型

interface searchFunc{
    (source:string,substr?:string):boolean
}
let sf:searchFunc = function(sr:string,sb?:string){
    return sr.length > (sb?.length || 0)
}
let sf2:searchFunc = function(sr:string,sb?:string):boolean{
    return sr.length > (sb?.length || 0)
}