JSFiddle - React, Tailwind, and code Playground

JavaScript

var point_a = [0, 0];
var point_b = [100, 200];
var coord = [50, 100];

function checkCoordinate(coord) {
    var slope = (point_b[1] - point_a[1]) / (point_b[0] - point_a[0]);
    var newSlope = (point_b[1] - coord[1]) / (point_b[0] - coord[0]);
    if (coord[0] > point_a[0] && coord[0] < point_b[0] && coord[1] > point_a[1] && coord[1] < point_b[1] && slope == newSlope) {
        alert('Yes! they are in the same line.');
    } else {
        alert('No :/');
    }
}
checkCoordinate(coord);