html2canvas/src/nodecontainer.js

function NodeContainer(node, parent) {
    this.node = node;
    this.parent = parent;
    this.stack = null;
    this.bounds = null;
    this.visible = null;
    this.computedStyles = null;
    this.styles = {};
}

NodeContainer.prototype.assignStack = function(stack) {
    this.stack = stack;
    stack.children.push(this);
};

NodeContainer.prototype.isElementVisible = function() {
    return this.node.nodeType === Node.TEXT_NODE ? this.parent.visible : (this.css('display') !== "none" && this.css('visibility') !== "hidden" && !this.node.hasAttribute("data-html2canvas-ignore"));
};

NodeContainer.prototype.css = function(attribute) {
    if (!this.computedStyles) {
        this.computedStyles = this.node.ownerDocument.defaultView.getComputedStyle(this.node, null);
    }

    return this.styles[attribute] || (this.styles[attribute] = this.computedStyles[attribute]);
};

NodeContainer.prototype.cssInt = function(attribute) {
    var value = parseInt(this.css(attribute), 10);
    return (Number.isNaN(value)) ? 0 : value; // borders in old IE are throwing 'medium' for demo.html
};

NodeContainer.prototype.cssFloat = function(attribute) {
    var value = parseFloat(this.css(attribute));
    return (Number.isNaN(value)) ? 0 : value;
};

NodeContainer.prototype.fontWeight = function() {
    var weight = this.css("fontWeight");
    switch(parseInt(weight, 10)){
        case 401:
            weight = "bold";
            break;
        case 400:
            weight = "normal";
            break;
    }
    return weight;
};