Answer 1

var arr = [2,7,11,15];
var target = 9;
var result = [];

arr.forEach(function(valOut,indexOut,selfOut){
	let arrRest = selfOut.slice(indexOut+1);
	arrRest.forEach(function(valIn,indexIn,selfIn){
		if(valOut+valIn===target){
			result.push(indexOut);
			result.push(indexOut+indexIn+1);
		}
	});
});

console.log(result);

Answer 2

@zhoujiamin 之前漏了，已修复哈。