Missing smallest positive integer

Write a function:
function solution(A);
that, given an array A of N integers, returns the smallest positive integer (greater than 0) that does not occur in A.

For example, given A = [1, 3, 6, 4, 1, 2], the function should return 5.
Given A = [1, 2, 3], the function should return 4.
Given A = [−1, −3], the function should return 1.

Write an efficient algorithm for the following assumptions:
• N is an integer within the range [1..100,000];
• each element of array A is an integer within the range [−1,000,000..1,000,000].

function solution(A) {
    // write your code in JavaScript (Node.js 8.9.4)
    let positive = []
    let count = 0
    for(let i=0; i<A.length; i++){
        if(A[i]>0){ 
            positive[ A[i] ] = true    
            count += 1
        }
    }
    //console.log("count: ", count)
    //console.log("positive.length: ", positive.length)
    //non-assigned positive[] will be populated automatically
    for(i=1; i<=positive.length; i++){ // = means that no missing in positive
        if( ! positive[i] ) return i
    }
    
    return 1
}