square.js

var square = 
`  +-+
    |
+-+-+
| | -
+-+-+`;
var points = [];
var jumpers = [];
var relations = [];
square.split('\n').forEach((line, lineIndex) => {
   line.split('').forEach((char, charIndex) => {
     if (char === '+') {
       points.push([lineIndex, charIndex]);
     }
     if (char === '-' || char === '|') {
       jumpers.push([lineIndex, charIndex]);
     }
   });
});
points.forEach(point => {
   jumpers.forEach(jumper => {
       if (
           (point[0] === jumper[0] && (point[1] === jumper[1]-1 || point[1] === jumper[1]+1)) ||
           (point[1] === jumper[1] && (point[0] === jumper[0]-1 || point[0] === jumper[0]+1))
       ) {
          if (relations.some(item => item[0] === point[0] && item[1] === point[1]) === false) {
            relations.push(point);
          }
       }
   });
});

// relations = (8 relations)
[[0,2],[0,4],[2,0],[2,2],[2,4],[4,0],[4,2],[4,4]]