纯JavaScript-数组值未定义

Question

I'm new to JS, please be merciful! I'm trying to implement some code, but I've run into a problem.

 var edges = [{src: 3, dst: 61}, {src: 46, dst: 40}, {src: 63, dst: 65}, {src: 1, dst: 50}]; var G = []; var min = 0; var mini = 0; var v; var m = 99; var n = edges.length; for (i = 0; i < m; i++) { G[i] = []; } n = edges.length; for (i = 0; i < m; i++) { G[i].push({ l: Infinity, previous: undefined }) for (j = 0; j < n; j++) { if ( edges[j].src == i ) { G[i].push( edges[j].dst ); G[i].sort(); } } G[i].unshift(i); } var Q = G; var u = []; u = Q[0]; var alt; Q[0].l = 0; while ( ( Q.length ) != 0 ) { for ( k = 0; k < m ; k++ ) { if ( Q[k].l < min ) { mini = Q[k][0]; u = Q[mini]; } } Q.splice(mini, 1); m--; for (i = 1; i < ( u.length ) ; i++) { alt = ul + 1; v = u[i]; for( j = 0; j < m; j++) { if(Q[j][0] == v) { console.log(v); console.log(Q[j].l); v = j; console.log(v); } } if ( alt < Q[v].l ){ Q[v].l = alt; Q[v].previous = u; } } mini = 0; } 

Here, I get an error in line 52, and it states that "Cannot read property 'l' of undefined in line 55". The value 'l' should be 99999999999999999999 by default, and yet, this disappears. I've been onto this for an hour, could you please help? Why do I get the undefined error?

Answer 1

I've found that if I'm using

G[i].push({ 
    l: Infinity, 
    previous: undefined 
  })

it is not possible to access 'l' or 'previous' by G[i].l , and thus, it is undefined. Instead I can access it by G[i][j]["l"] , since

{ 
  l: Infinity, 
  previous: undefined 
}

is an element on its own, and I have to access its elements.