interact.modifiers.snap({
  targets: [{
    x,
    y: 75,
    range: Infinity
  }]
})

interact.modifiers.snap({
  targets: [(x, y) => {
    return {
        x,
        y: (75 + 50 * Math.sin(x * 0.04)),
        range: Infinity
    };
  }]
})

interact.modifiers.snap({
  targets: [(x, y) => {
    return {
        y: x % 100 < 50? 50: 100,
        range: Infinity
    };
  }]
})