Js the number of different paths

Ideas:

1. If it is only one line or a situation, it would have only one path
2. If the diagonal position, there is at first a right rear (start-> A-> C) and the lower rear to right (start-> B-> C) two pathways as shown below:
   
3. And so on, we can conclude that the total number of paths each path is the path to the left position below the plus
   

function short(m, n) {
    var i,j;
	let dp=new Array(n).fill(0).map(x=>new Array(m).fill(0));
	for(i=0; i<m; i++) {
		dp[0][i]=1;
	}
	for(i=0; i<n; i++) {
		dp[i][0]=1;
	}
	for(i=1; i<n; i++){
		for(j=1; j<m; j++){
			dp[i][j]=dp[i-1][j]+dp[i][j-1];
		}	
	}
	return dp[n-1][m-1];	

}
console.log(short(7,3));