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JavaScript

var svgString = a='<svg width="612" height="394" xmlns="http://www.w3.org/2000/svg"><g>     <title>Layer 1</title>     <rect id="svg_1" height="152" width="265" y="44" x="91" stroke-width="5" stroke="#000000" fill="#FF0000"/> </g> <g>     <title>Layer 2</title>    <rect id="svg_2" height="125" width="151" y="157" x="399" stroke-width="5" stroke="#000000" fill="#FF0000"/></g></svg>',
    tempElement = document.createElement('div');

tempElement.innerHTML = svgString;
var height = tempElement.querySelector('g:nth-child(1) rect').getAttribute('height');

var text = '<svg width="612" height="394" xmlns="http://www.w3.org/2000/svg"><g>     <title>Layer 1</title>     <rect id="svg_1" height="152" width="265" y="44" x="91" stroke-width="5" stroke="#000000" fill="#FF0000"/> </g> <g>     <title>Layer 2</title>    <rect id="svg_2" height="125" width="151" y="157" x="399" stroke-width="5" stroke="#000000" fill="#FF0000"/></g></svg>';
var d = text.getAttribute('height');
alert(d);